I had this same issue happening as well and I basically gutted my project to get to the bottom of it and came to find out it was another asset causing the problem.
In my case it was Suimono water system. Now once I found out it was this causing it I did test and found that it was only causing the problem when I had it active in the scene once I disable the game object PM returned back to functioning ability. So for those having the problem check other assets they might be calling the focus from PM when typing in the state rename or fsm rename fields. Hope this helps