Setup: 2011 i5 Mac mini attached to a Yamaha RX-A700 outputting to a Sharp LE632U
I initially thought this was the "Best resolution for display" setting misinterpreting the res when turning off my AV equipment. In System Preferences, I disabled this and have set it for 1080p, then 1080i. Every time I turn off the AV equipment for a few hours and come back, when I turn it on, it's stuck on that blue screen that flashes when you connect an external display on any Mac. The TV also indicates that it's at 1 resolution lower than what I happened to set it to before I turned it off.
That is to say:
1080p becomes 1080i
1080i becomes 720p
Background processes still work, I can still SSH in. Screen Sharing or vnc DO NOT work, which I find odd.
Anyway, hoping someone else out there has seen something like this. All worked well in Mountain Lion.
I had the same problem. Solved it with HDMI Detective. Wasn't very happy that it cost me a not-insignificant amount of money to solve the problem. The apple forums have a few long threads on this issue with absolutely no help from Apple.