A list manager here decided that the list admin email address should be set to the list bounce address.
Later, a message was sent to this address informing the admin that there were requests pending approval/whatever. Mailman then accepted this message and attempted to parse it as a bounce message which, obviously, failed. This failure was then send to the list administrator informing them that a bounce message could not be parsed. This was repeated until python coredumped the bounce queuerunner process.
Logged In: YES
user_id=1123998
Originator: NO
Fixed in Mailman 2.1.10.