Lo and behold, I found the answer, which is that I'm dealing with a bug here. Of all places, it was in the How-Tos (yes, I've looked there before) http://www.zope.org/Members/gtk/containers Given the number of replies, I have to assume that few knew (or at least remembered) this. So I'm posting this info in case anyone is suffering the same problem. ^_^ - Gregor