0x7fffffff is right - the problem was actually somewhere else:
I was adding nested views to the 'root view' but did not add their view controllers as a child too, i.e.
I was doing:
[_ContainerView addSubview:_ViewControllers[tabId].view];
without
[self addChildViewController:_ViewControllers[tabId]];
It's now fixed - thank you for testing this 0x7fffffff.