Windows/NTFS/Change of Permissions

I have an odd one and I am not sure this is related to expat but I wanted to
see if anyone else has run into this.  We're running on a Windows platform
with NTFS.  We're opening files via expat as xml.  After saving an xml file
and then reopening the file(it is at the point of reopening) we see a change
of user permissions on the file.  The user permission is now locked
exclusively for that user on the Windows platform and cannot be accessed by
any other users on the PC.  If we save in an alternative file format(not xml
and not using expat to open the file) we do not see a change in user
permissions.  Anyone seen this one before?  At this point I cannot point to
the problem being expat but it is suspicious that it doesn't happen when the
same data is stored using another file format.  Also note that only one of
our users is seeing this behavior-otherwise it is fine for all users.