Yup, this is a known issue that we very recently just figured out and fixed. Ended up being a *very* tricky issue to re-produce as it only happens in a very specific circumstance. The bug ID is CSCec86400 which you probably will not be able to view from Bug Toolkit. Go ahead and open a TAC case and tell them you ran into this problem. They will be able to post the interim image (based on 6.3(4)) for you.
