Members of umbrella list receive double-posts

Consider list1 and list2 both on the same Mailman server. An umbrella list, list3, has both lists subscribed.

Users who are on both list1 and list2 will receive double copies of mail sent to list3. This is a FAQ'd problem with various workarounds; it should be fixed so that the workarounds aren't needed.

http://www.python.org/cgi-bin/faqw-mm.py?req=show&file=faq03.005.htp