We've been having some issues with that, and I cannot pinpoint which side the fault is on. Is concurrent editing of a word document by multiple users with "edit in office" feature of confluence supported or not? Microsoft says:
The new co-authoring functionality in Microsoft Office 2010 makes it possible for multiple users to work productively on the same document without intruding on one another’s work or locking each other out.
You can use this new co-authoring functionality in Microsoft PowerPoint 2010, Microsoft Word 2010, and Microsoft OneNote 2010 documents on SharePoint Server 2010. New co-authoring functionality is also supported in Excel Web App and OneNote Web App.
So it sounds like it is proprietary SharePoint feature. Is that so?