[2007] Links to Excel breaking

Hi,

I have an excel file and a presentation, both placed in different
directories on a network share mapped to a network drive. I then copy
a graph or a spreadsheet range from the .xls file to the presentation,
using Paste Special - Paste Link. I check the link in the Edit Links
dialog and it shows the absolute path to the object ("\\network\share
\directory\file.xlsm!sheet[file.xlsm]sheet chart_id"; don't ask me why
it's like that). All's good, so I hit save and close the presentation.

I then reopen the same presentation immediately and check Edit Links
again. in 2/3 (?) of the cases the path element of the link I just
pasted will now be truncated, and the link will show as relative
instead. Attempts to update it (manually or automatically) will fail
as the linked file is in a different directory. If I hit Change Source
and navigate to the right file, the path will fix itself (though
usually still remain relative, ie. "..\file.xlsm") and the link will
subsequently work all the time.

Has anyone seen this bug? Is there a way to avoid it? The files need
to stay in different directories for reasons that are beyond my
control I'm afraid.

Best regards,

Karol Kozimor