I am trying to write XML spreadsheet documents programmatically. However,
there seems to be a bug when Excel reads the XML spreadsheet and parse the
HRef attribute of a Cell.

I am having this problem for relative paths. If I have
'Parent/Child/file.txt' and I assign an HRef attribute for it Excel on
Windows machines adds extra folders to the path resulting in
'Parent/Child/Parent/Child/file.txt'.

This looks like a bug. I tried opening the same XML spreadsheet on the Mac
version of Excel and it works fine. I tried opening it on OpenOffice Calc and
it works perfectly. I tried adding dots and slashes to the path but nothing
worked.

Any ideas?