I wonder if Francis has his information right on O'Brien.
The Marlies announced signing him to a contract on July 3rd:
http://marlies.ca/article/marlies-sign-seven-players
While the AHL contract doesn't prohibit him from signing a PTO with the Flames, it is just weird to see someone signed with one teams AHL affiliate attend another NHL training camp. But I suppose the promise of guaranteed ice time in a preseason game or two could make it happen.