1. Create a writer document;
2. Insert a 2 rows 2 columns table;
3. Right click in the table and choose "table..." in the context menu;
4. In the line style listbox in Border tab, choose "6.55 pt";

You can see in the preview area, all the horizontal Lines are double lines, the
upper is a bold line and the lower is a slim line. For the vertical lines, left
is bold and right is slim.

5. Click OK to apply the borders.

You can see the result is different from the preview just now. Only the
horizontal line on the top is upper-bold and lower-slim, the others horizontal
lines are upper-slim and lower-bold.

It seems it achive a outer-bold and inner-slim border, but the 2nd horizontal
line isn't accord with the item we choose.

There is a scenario:
If a user want to make a table which only have a bottom border(This offen used
in  the heading of some official documents in China). He want a upper-bold and
lower-slim double line. So (s)he choose 6.55 pt in the border line stype listbox.
After (s)he click Ok button. (s)he get the opposite result: upper-slim and
lower-bold.