I've just had a chat with Emil. I was using the last Jitsi nightly, he was using Hangouts on Android. The first problem was that each time he sends a message the resource is changed to the bare JID. Then even if I manually select the Android resource, the message is still sent to the bare JID (as Emil was receiving it on all his devices).
Could you please have a look? Could these be related to the Hangouts behavior?
I think that at least the second problem could be an issue in Jitsi.