I found a bug when playing a mpmovieplayerviewcontroller inside a full screen modal.
Line 578 of mgsplitviewcontroller.m reads:
[_hiddenPopoverController presentPopoverFromRect:CGRectZero inView:self.view permittedArrowDirections:UIPopoverArrowDirectionAny animated:NO];
but this causes a crash if self.view is not attached to a window.
So I added
if (self.view.window != nil)
before that line and that worked.