<message type="chat"> from unknown gateway JID displays "broken image" icon

If Gajim receives a "chat" type message from a JID that is not in the roster, then in the contact list shows no icon (instead of the grey "man" icon normally shown for an unknown/offline contact) and the banner in the chat window shows a page with a red "x" on it (the "broken image" image).

I'm still trying to figure out what causes this behaviour. It only happens when a new message comes in through the cheogram.com gateway... and I've a had a couple theories, but even when I make the stanza XML identical to that coming in from Psi, the behaviour is different. I'm really at a bit of a loss.