=== modified file 'Mailman/MailList.py'
--- Mailman/MailList.py	2007-11-26 01:32:26 +0000
+++ Mailman/MailList.py	2008-02-23 23:14:01 +0000
@@ -1062,9 +1062,10 @@
         newaddr = Utils.LCDomain(newaddr)
         Utils.ValidateEmail(newaddr)
         # Raise an exception if this email address is already a member of the
-        # list, but only if the new address is the same case-wise as the old
-        # address and we're not doing a global change.
-        if not globally and newaddr == oldaddr and self.isMember(newaddr):
+        # list, but only if the new address is the same case-wise as the
+        # existing member address and we're not doing a global change.
+        if not globally and (self.isMember(newaddr) and
+                newaddr == self.getMemberCPAddress(newaddr)):
             raise Errors.MMAlreadyAMember
         if newaddr == self.GetListEmail().lower():
             raise Errors.MMBadEmailError
@@ -1120,9 +1121,16 @@
             raise Errors.MembershipIsBanned, pattern
         # It's possible they were a member of this list, but choose to change
         # their membership globally.  In that case, we simply remove the old
-        # address.
-        if self.getMemberCPAddress(oldaddr) == newaddr:
-            self.removeMember(oldaddr)
+        # address.  This gets tricky with case changes.  We can't just remove
+        # the old address if it differs from the new only by case, because
+        # that removes the new, so the condition is if the new address is the
+        # CP address of a member, then if the old address yields a different
+        # CP address, we can simply remove the old address, otherwise we can
+        # do nothing.
+        if self.isMember(newaddr) and (self.getMemberCPAddress(newaddr) ==
+                newaddr):
+            if self.getMemberCPAddress(oldaddr) <> newaddr:
+                self.removeMember(oldaddr)
         else:
             self.changeMemberAddress(oldaddr, newaddr)
         # If globally is true, then we also include every list for which
@@ -1144,8 +1152,10 @@
             mlist.Lock()
             try:
                 # Same logic as above, re newaddr is already a member
-                if mlist.getMemberCPAddress(oldaddr) == newaddr:
-                    mlist.removeMember(oldaddr)
+                if mlist.isMember(newaddr) and (
+                        mlist.getMemberCPAddress(newaddr) == newaddr):
+                    if mlist.getMemberCPAddress(oldaddr) <> newaddr:
+                        mlist.removeMember(oldaddr)
                 else:
                     mlist.changeMemberAddress(oldaddr, newaddr)
                 mlist.Save()