I think this may be re-hash, apologies if so.
Several people have told me Cisco IOS 'used' to have a
well-known bug related to route-reflectors (clients), where
they would ignore BGP withdraw messages and continue to
announce routes (including full original AS path).
I can duplicate this type of problem with one upstream
provider (but not the other), I am trying to help them help
me (as they seem to be somewhat at a stand-still resolving
the problem). So far I've only gotten somewhat vague
information, and haven't been able to find anything specific
Any pointers (Cisco bug ID, IOS releases with the problem
and those that fixed it, etc) would be helpful.