In a previous patch for MS Office, Microsoft removed support for custom XML according to an article from Computerworld. This is a result of an injunction i4i won against Microsoft. It prevents Microsoft from selling Word with custom XML support. Microsoft is currently working on a Mac update for Office that will remove it also. Microsoft has not given any information on when the patch will be released.
The patch release does not have to be installed if you bought your copy of Office before Jan 10. The case against Microsoft was filed in 2007, and the injunction was issued on Oct 10, 2009. The court gave Microsoft only 6 days to remove the capability from Word. An appeals court suspended it while they heard Microsoft plea for needing more time to remove the functionality from Word. Microsoft was allowed 5 months. Microsoft was able to release the patch by the Jan 11, 2010 deadline, but are still working on the Mac match. Even though the Mac version of the software was not included in the injunction, they are removing the capability from Word to prevent concerns about complying with the injunction. Microsoft has stated that the preview version of Word 2010 and Office 2010 do not need to be patched.
I expect Microsoft to appeal this decision by the courts. This issue will take many more years before a resolution is reached.