A few articles have cropped up in the last couple of days on Office 2007's "failing" OOXML compliance tests. If you're interested in reading up on that, perhaps you'd like to start with the slashdotting of it.
Well, the whole point of moving a proprietary file format into open standardization is that the format is controlled by the standards body and gets changed along the way. This has already happened with OOXML, and this is the reason for the apparent non-compliance. So this "failure" is actually a success. Or, to quote Run D.M.C., "Not bad meaning bad, but bad meaning good."
A more precise explanation, with background information, can be found here.