Ok - this has now been proven to be a bug inside MS, with a simple repro. Alex - let me know if you want to push for a hotfix for this and I'll give you the internal bug number that's been opened that you can use when you call PSS (and some high-level names to add to make sure you get the correct response).
Thanks for posting about this (and Gail, thanks for pulling me in).
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