After some minor delays and a recent "now you see it/now you don't" routine on Xbox Live, the Dragon Age: Origins DLC, Return to Ostagar, seems to have introduced a new bug to those who picked up the most recent title update. According to a BioWare forums post by community manager Chris Priestly: "This morning a title update on the Xbox 360 for Dragon Age: Origins was made available in preparation for the release of Return to Ostagar ... this title update introduced a previously undetected issue that causes specialization classes to not work correctly."
Additionally, he apologizes to those affected and notes that the DLC has been removed from Xbox Live "until the issue is resolved." We're also ensured that more information will be provided on this as soon as it's available. Oh, and in case it wasn't already apparent -- if you're thinking about downloading the title update, you probably shouldn't.