[Zope] MSword-webdav question

Hi all I have Zope 2.5 (started with option: W -9800) on win2k and Office XP. I can open/read/modify MSWord documents via WebFolder, but if I open-modify-save-close a document, and then I reopen it, it appears read-only and only after some time I can reopen and modify it. Can anyone help me to understand what happens after I modify a document the first time and why it remains locked for some time and what unlock it? Michele