List-* field handling for nested lists

RFC 2369 (http://tools.ietf.org/html/rfc2369#section-4) and RFC 2919 (http://tools.ietf.org/html/rfc2369#section-7) specify the handling of List-* fields in nested lists. In my recent experience Mailman 2 handles List-Post and List-ID incorrectly. I suspect that Mailman 3 probably does the same.

According to the RFCs List-Post should be left alone and a new one not added, and a new List-ID field should be added when there is already one, but in both cases Mailman 2 replaces an existing field's contents with data for the child list.

RFC 2919 specifies that if the existing List-ID is not a parent list (eg, somebody resent a message from an unrelated list to this one, or reposted from a nested list to a parent), then it should be removed. RFC 2369 doesn't say that explicitly (I didn't check very carefully, though), but I think it should behave the same way: existing List-* fields that aren't from a parent list should be removed.

ISTR there is at least one more RFC for List-* fields, should check.