When a user double clicks on another user in group chat (or right clicks and selects Start a chat), nothing happens. Also, if another user using older version of Spark sends a private message to a user on 2.9.0+ version, such message doesn't appear (no popup, no tab opened).
I can see the message appearing in the Raw Received Packets window in Spark debugger. Spark for some reason is not creating a tab for this.