Consensus (without proving it yet) is that this looks like a bug. Do you want to push for a hotfix if that turns out to be the case? If so you'll need to call in to Product Support and they'll pick it up. if not, they'll at least investigate and confirm, and then get it into the next release.
Thanks
Paul Randal
CEO, SQLskills.com: Check out SQLskills online training!
Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005