Black screen when playing vid in iTunes, need be reselect "My Computer"...

Just trying to iron out a few annoyances with the AppleTV and my library. I have converted a fair few TV shows and movies now, they all play nice on the ATV. Things are going fine. The only problem I have at the moment is that when I play a file in iTunes I get audio, and a black screen. When I check the airplay option it shows "My Computer" is selected, I then have to select the AppleTV, and then reselect My Computer and it plays fine. It seems like its almost defaulting to airplay, although the audio playback and airplay icon contradict this. Any ideas? Is there a setting somewhere that I'm missing?

Seems to have fixed itself since the recent iTunes update. Cannot explain it!...