When I try to initiate a video to play (via YouTube) in a UIWebView, the video opens, then the debugger says:
[MPAVController] Autoplay: Enablin
I just had this very same issue in one of our apps. Turns out we were setting the UIWebView's HTML to an empty string in -(void)viewWillDisappear. Apparently this method is now being called in iOS 6 when displaying a fullscreen video from an UIWebView, so that's probably where your issue comes from.