Microsoft webfolders WebDAV incompatibility issues

Zope offers an almost complete and compliant WebDAV implementation.
However we run into some compatiblity related problems
when we use Zope through webfolders under Windows (XP) and
Microsoft problem. It is a very common problem that Office
complains that a file is read-only when trying to save the file.
We figured out that Microsofts WebDAV implementation requires
an ETAG header to work correctly. However this does not seem to work
on all Windows installations. Reverse engineering Microsofts 
behaviour on the protocol level is nerving. Does anyone has 
similiar problems or any additional thoughts and tips on that issue?

Andreas Jung