After reconnect some messages from MUC appear in a private chat from this MUC

Gajim git master 31417ffb
python-nbxmpp git master 0aed44470

How to reproduce:

start a private chat with romeo from a MUC
exchange messages
disconnect account
be long enough offline to ensure some messages get posted in that MUC
reconnect
messages from all except romeo appear in the MUC, the ones from romeo only in the private chat.