Please attach such a .svg picture.

Created attachment 85079 [details]
test SVG file

This is the svg file I used in my testing.

I was unable to reproduce this issue on an alternate configuration of Windows 8.1 Enterprise with Writer version: AOO420m1(Build:9800)  -  Rev. 1692551

I used the attached .svg file and tried with various x values for the text node and its tspan elements.  I used:
0 and 10 for x in text and tspan.  
0 and 10 for dx in tspan.
No x or dx for either text or tspan.

It is a simple file, but it does use text-anchor=”middle” and has multiple tspan elements.  It is possible that a more complex SVG file is needed with another attribute in combination with text-anchor=”middle” to reproduce the issue, but I was not able to test for it.

For all the variations I used of this file Writer displays the text for each line of the image as expected: while using text-anchor=”middle” the center of the text is anchored to the position defined by the x attribute (without an x attribute 0 is used for the first line and subsequent lines use the end of the previous line)

Created attachment 85081 [details]
svg showing alignment issue

I have now reproduced this issue on my configuration (Win8, AOO420)

After my last update I received an email from Clive (original reporter).  He said he was unable to get into Bugzilla, and gave me more information on his issue.

From Clive: “You can exaggerate the effect on your example if you 1) shorten the text in each part to a single letter such as I, H or O, and 2) increase the font-size.
My original problem stemmed from a ‘pretty’ layout of tspan elements: a line-break between them acted as a space and screwed up the cantering. You can overcome this by having line-breaks only within parameter attributes or not at all. But Writer still persists to misalign the characters, except for the last tspan in a text element.”

The issue is a little more subtle than I originally thought, and it is present in my text.svg file.  To make it more obvious I:
   Created Letters.svg with 3 lines of the letter H at 48 pt font
   In Writer I inserted Letters.svg through the menu (Insert->Picture->From File…)
   My viewing in Writer shows all but the last line to be ~1/4th the character width to the left of center. 

He also suggested using more images at http://chordography.blogspot.com/.

Created attachment 85084 [details]
svg with misaligned text with & without line breaks

Top (red) image shows misaligned text with line-breaks between tspan elements. Lower (green) image is identical except line-breaks occur only within the parameter sections, which should not interfere with spacing.

All major browsers, even IE, show misaligned text only in the red image (with line-breaks), while Writer produces similar misalignment in both red and green images.