MSN transport: messages go out but won't come in

OK, I’ve got a simple Smack app that starts up a chat session and just keeps it live so I can see text go in and out. I started with a local Jabber account, then a Yahoo account, then a AIM account, and they all worked great. But when I put in an MSN account, it sends the message just fine, but when I send a message back in, it doesn’t make it back to the chat session.

I enabled the debug log and the message does get to the server, but never gets processed by the MessageListener.

Each MSN account lists the other as a friend.

Any suggestions?