The artificial horizons in the OH-6A and CH-34 both behave in strange ways. For the former the issue is that the horizon centre (the white circle with the hole in the middle by my assumption.) is many degrees off on the vertical axis, meaning that only the bottom of the centre ball is visible when level. To line the horizon line up with this point requires the helicopter to be nearly stood on it's tail. in the CH-34 the horizon ball is level and in it's place but the expected results of moving the helicopter around are inverted causing the ball to shift into the climb position when the nose is dropped and the dive position when the nose is raised.
Neither issue is game breaking and in the CH-34 it is still possible to hold a hover, and though it is perfectly possible to hold a hover in the loach during daytime, I imagine (I don't really fly them in all honesty) that in darkness when hover targets are not visible, maintaining a level is very difficult.