This is not a Mailman bug. The text sent in the rejection notice when generic_nonmember_action is Reject is specified by the list owner as nonmember_rejection_notice. The text you quote is merely the default if the list owner chooses not to provide other text.
This is not a Mailman bug. The text sent in the rejection notice when generic_ nonmember_ action is Reject is specified by the list owner as nonmember_ rejection_ notice. The text you quote is merely the default if the list owner chooses not to provide other text.
You should take this up with the list owner.