On iPad Mini, AppleTV doesn't work with Google Hangout video chat every time we try to use Apple TV with Google Hangout on our Ipad Mini (with the Google hangout app)  the screen goes blank the second the video chat window shows up. 

Up to that point, Apple TV mirrors everything perfectly (other apps, videos, internet, etc). Is this a bug or  some kind of device limitation that prevents Hangout on the Ipad Mini? we already downloaded all the updates both on the iPad mini and the Apple TV console. Our Apple Tv/ Hangout setup does work on the same rig when we use a Mac Mini computer.

Many thanks
I googled around for it, but all I found was this question asked with the same words on other fora.

The second link has someone giving the answer I thought likely: the app disallows AirPlay. Some app makers don't want you to watch their iOS content on your TV. HBO Go was a notable example, but they updated their app to allow AirPlay streaming to AppleTV in February 2013 (see here). While I can't find any documentation that the Google Hangout iOS app does not allow AirPlay, the behavior you describe is at least consistent with that hypothesis.