Here's a confusing factor.

I checked my copy of the Unicode 4.0 specification, and it shows U+25AA and +25AB as being much smaller than the corresponding larger flavors at, say, U+25A0 and +25A1.  

And the online code table (current with Unicode 8.0) also shows the small (actually, tiny) forms at http://www.unicode.org/charts/PDF/U25A0.pdf

On Windows 10, I opened the Windows built-in Character Map utility and checked the OpenSymbol font.  The size differences are in conformance with the Unicode specification, with U+25AA and U+25AB (Black and White Small Square) showing quite small.  The same is the case when I check Arial Unicode MS, although that font has them all seem somewhat smaller in the Character Map tool.  Times New Roman also has tiny 25AA and 25AB.

In all of these, the U+25AA-25BB are smaller relative to the larger ones than they appear in the uploaded Windows7_OK.png.  It is much more akin to the Windows 10 display.

I don't have an answer.  Only an indication that this situation may be more complex than first appears.

Please compare the characters between the attached pictures. There are very different hands and phones. => The pictures shows 2 different character sets/fonts. If the same font file is installed, it seems that windows makes a font substitution. Why? I don't know …

Test with character U+261A (aka “Black Left Pointing Index”)
This char exists in font “Segoe UI Symbol” + “European Pi Std 3” + “DejaVu Sans”

In Writer, under Windows 7:

[Selected font -> font displayed -> font in exported PDF]
Segoe UI Symbol -> Segoe UI Symbol -> Segoe UI Symbol
European Pi Std 3 -> European Pi Std 3 -> European Pi Std 3
Times New Roman -> DejaVu Sans -> DejaVu Sans
Arial -> DejaVu Sans -> DejaVu Sans

So font “European Pi Std 3” is correcly used in OO under Windows 7
If char doesn't exist in a font, font is replaced with font “DejaVu Sans”

In Writer, under Windows 10:

[Selected font -> font displayed -> font in exported PDF]
Segoe UI Symbol -> Segoe UI Symbol -> Segoe UI Symbol
European Pi Std 3 -> Segoe UI Symbol -> European Pi Std 3 (but rendered incorrectly)
Times New Roman -> Segoe UI Symbol -> Segoe UI Symbol
Arial -> Segoe UI Symbol -> Segoe UI Symbol

Even if char EXISTS in font “European Pi Std 3”, the font rendered in Writer is Segoe UI Symbol.
If you export the Writer document to PDF, font “European Pi Std 3” is used, but with incorrect size/space: char is larger then its "box" as it was reserved for “Segoe UI Symbol”)
If char doesn't exist in font, font is replaced with font “Segoe UI Symbol”

Note that “European Pi Std 3” is correclty displayed in MS Word.
This means that EXISTING characters in fonts European Pi Std 3 are replaced by “Segoe UI Symbol” as if they didn't exist in “European Pi Std 3”. Really strange...

Created attachment 85307 [details]
Exported from Writer to PDF under Windows 7

Created attachment 85308 [details]
Exported from Writer to PDF under Windows 10

I Attached exported PDF files

You can see that under Windows 7 the font European Pi 3 is correclty used

You can compare with font preview:
http://www.fonts.com/font/linotype/linotype-european-pi/3

Btw, this also means that, under Windows 10, the character map in Writer -> Insert Special Characters shows Segoe font chars instead of European Pi 3

If you go to http://www.fonts.com/font/linotype/linotype-european-pi/3
than select Character Map > Miscellaneous Symbols (or Geometric Shapes)
you'll see generated picture of the font chars as they should be

(In reply to laurent.hosch from comment #8)
> If you go to http://www.fonts.com/font/linotype/linotype-european-pi/3
> than select Character Map > Miscellaneous Symbols (or Geometric Shapes)
> you'll see generated picture of the font chars as they should be

Those are enlarged images of the character glyphs (although minimum sizes are also shown, it seems).

In any case, AOO is a Unicode application and how a commercial font foundry renders Unicode in contrast to the Unicode specification illustration for those code points is the font foundry's to deal with, not AOO.  

However, it appears that font substitution is happening in the problems at hand, and we do need to understand that.  Troubleshooting and confirmation is a problem if we are talking about a commercial font.

When I install the supplied European Pi Std 3 font and inspect it using the Windows 10 Character Map Accessory tool, I see U+25AA and U+25AB as having very small glyphs, especially in contrast to U+25A0 and U+25A1.  When I paste those characters into a Microsoft Word 2016 document, the font is preserved and the difference in sizes is as well.  Pasting the same characters into AOO 4.1.2 Writer shows no difference from the other two renderings.  And the agreement with the Unicode 4.0 and 8.0 specifications is extremely close.

Based on this, it appears that AOO is not doing anything that interferes with the correct rendering of these Unicode code points.  There is agreement among the Unicode specification, the Windows 10 Character Map view of the font, the rendering in Word 2016, and the rendering in AOO 4.1.2 Writer.

(The result with a PDF will depend very much on whether or not the necessary font definitions are exported into the PDF or not among other factors.)

Created attachment 85309 [details]
Windows 10 Character Map Presentation

This shows, in the "Characters to copy:" field, the Windows 10 rendering of glyphs for code points U+25AA, AB, A0, and A1 with the installed European Pi Std 3 font.  This is to establish a baseline of how the characters are rendered in applications, before considering what happens on export from those applications to PDF.

Created attachment 85310 [details]
Word 2016 Rendering of the 4 Characters from Attachment 85309 [details]

This shows the glyphs rendered by Word 2016 for the four characters with code points U+25AA, AB, A0, and A1 in the Windows 10 Character Map for the European Pi Std 3 font.  Note that the correct font is applied and rendering is at 11.5 pt.

Created attachment 85311 [details]
AOO 4.1.2 Writer Rendering of the 4 Characters from Attachment 85309 [details]

The pasting of the same 4 selected characters into an AOO 4.1.2 Writer document also demonstrates the dramatic difference in size between the codes for small boxes (U+25AA and +25AB) and the plain (large) ones.

In this screen capture, the text area is zoomed to 200% to demonstrate the clear differences.  

Also, note that the Unicode specification for these glyphs does show the smaller ones centered vertically, unlike the Word 2016 rendering, which also seems to have the small boxes a bit too large, in comparison with the Character Map and the Writer form.

So there are some deviations to wonder about, on closer examination.

Still, from this relatively stable situation, one can attempt to isolate what other deviations there are.

Created attachment 85312 [details]
Linotype description of the glyphs that have been expected

This screen capture shows, in left to right, the glyphs presented on the Linotype page for the European Pi Std 3 font.  Note that 25AA and 25AB are larger than all but in the Word 2016 presentation, and they are also on the character baseline rather than centered vertically, also as only rendered by Word 2016.

(I missed this earlier, until I had screen shots to compare.)

Hmm I think that the font actually rendered on screen (in Windows Charater Map and AOO) is not the installed commercial font “European Pi Std 3” but “Segoe UI Symbol” instead.

In Word 2016, the font displayed is really “European Pi Std 3”.

Have a look to unicode character U+261A (aka “Black Left Pointing Index”), we can clearly noticed that the font “European Pi Std 3” is substituted for “Segoe UI Symbol”.
When I compare the other chars (25A0, 25A1, 25AA, 25AB), I think they are also replaced on screen by “Segoe UI Symbol” (in Windows Charachter Map and AOO), which could explain the difference of sizes and position. I think that these 4 unicode charachters, like the hand charachter, are substitutions (on screen). Maybe this is something to do with Windows 10?

… and again, this issue only appears in Windows 10, not in Windows 7 (with exactly the same versions of AOO, Word…)

The PDF at <http://www.unicode.org/charts/PDF/U25A0.pdf> provides what the Unicode Standard presents as glyphs for code points U+25A0, 25A1, 25AA, and 25AB in the first column of the grid.  This has been consistent from Unicode 3.0 to 8.0 (2015).  The small boxes are significantly smaller than the larger ones and centered vertically in the line.

PS: LibreOffice 5.0 x64 on Windows 10 shows the four characters in exactly the same form as the AOO 4.1.2 Writer Rendering. 

Concerning Substitutions:

The Linotype font "European Pi Std 3" does not appear to provide glyphs for all of the Unicode code points in these blocks of symbols. The pointing finger is different, pointing downward in Word 2015 and in the Linotype illustration.  In the Character Map and OpenOffice it is straight or with the tip upward a little.  The Unicode version is a bit more elaborate.

So one hypothesis is that substitutions are being made even where the Linotype font has glyphs for the code points, but Word does whatever is needed to get that right?  And in Windows 7, there was no problem.  Hmm.  Is that true with AOO 4.1.2?

Interesting problem.

(In reply to orcmid from comment #16)
> The Linotype font "European Pi Std 3" does not appear to provide glyphs for
> all of the Unicode code points in these blocks of symbols.

Do you talk about code points U+25A0, 25A1, 25AA, and 25AB as well? If so, how could you be sure that the Linotype font "European Pi Std 3" does not provide glyphs for these symbols? As you said, Word renders these chars exactly like on the Linotype page.

Weird...

Created attachment 85313 [details]
AOO 4.1.2 rendering both fonts under Windows 7

Under Windows 7, AOO 4.1.2 renders glyphs for font “European Pi Std 3” (they are exaclty the same as those on the Linotype web page) in last column

I added glyphs from “Segoe UI Symbol” in the left column for comparison
(Under Windows 10, all these “European Pi Std 3” glyphs appear to be replaced with those from “Segoe UI Symbol”).

Created attachment 85314 [details]
AOO 4.1.2 rendering fonts under Windows 10

Here you can see that all “European Pi Std 3” glyphs are replaced with those from “Segoe UI Symbol” in AOO 4.1.2 under Windows 10

I'm afraid this nothing to do with AOO but Windows 10 :-(

It's a bit like: “Windows decides” but “any versions of Microsoft Word bypass the rules (defined by Windows)”

Or is it just an issue in Windows itself...

(In reply to laurent.hosch from comment #17)
> (In reply to orcmid from comment #16)
> > The Linotype font "European Pi Std 3" does not appear to provide glyphs for
> > all of the Unicode code points in these blocks of symbols.
> 
> Do you talk about code points U+25A0, 25A1, 25AA, and 25AB as well? If so,
> how could you be sure that the Linotype font "European Pi Std 3" does not
> provide glyphs for these symbols? As you said, Word renders these chars
> exactly like on the Linotype page.
> 
> Weird...

No, I did not mean the glyphs for code points that Linotype lists glyphs for.  It is clear that the Linotype font has glyphs for U+25A0, 25A1, 25AA, 25AB.  It is that their not providing glyphs for all the code points in the Unicode blocks of interest that might be relevant.

There might also be something related to registration of proprietary fonts, also, but I am not at all clear how that would show up.

(In reply to laurent.hosch from comment #20)
> I'm afraid this nothing to do with AOO but Windows 10 :-(
> 
> It's a bit like: “Windows decides” but “any versions of Microsoft Word
> bypass the rules (defined by Windows)”
> 
> Or is it just an issue in Windows itself...

It certainly appears to be a Windows 10 case.  

We cannot rule out that there may be some changes in Windows 10 API behaviors, possibly with alternatives.  It might also be related to libraries that AOO might be relying on for some aspect of font handling, although it is strange that the Windows 10 Character Map shows the same results that AOO 4.1.2 provides.

Out of curiosity, I did the same thing with the Character Map, Select, and Copy of the four characters (U+25AA, AB, A0, A1) into an opened WordPad document. LO!  Even though I had changed the font to European Pi Std 3, the pasted characters are revealed as Segoe UI Symbol in WordPad.  And when I select the characters and manually change the font to European Pi Std 3, there is no change.

Another interesting factor is that Word Pad does not provide the spelled name of the European Pi Std 3 in its font dropdown list.  I can see where it is, between "Eras Medium ITC" and "FELIX TITLING" on my system, but the letters of the font name are all x-d out.

So there is indeed something about that font that Windows 10 fixtures don't like, at least some of the time.

more and more strange...

European Pi Std 3 is listed correclty in the font dropdown list in WordPad under my installed version of Windows 10