iChat had the ability to auto-join jabber chat rooms, but Messages 7.0 seems to have lost that functionality. Anyone know if there is a
defaults write … command to either auto join specific chats, or to re-enable the auto-join feature?
This worked for me: I signed into iMessage with my Apple ID, and suddenly I didn't have to click "Rejoin Chat" anymore.
Here's the kicker - when I signed out of iMessage, it continued to work... I have no idea why.