I have a to-be pit of death on one of my levels. It is setup so that before I add the death triggers, it's an actual pit with a floor. However, when the backdrop objects (set to 'obstacle') ar 16 pixels or more lower than the frame boundary, they stop acting as obstacles. The player just falls right through as if it were just a normal backdrop.
EDIT: I found a workaround. I just put a detector at the top that knocks out the horizontal movement, and threw in the death trigger at the bottom. Weird that the collision tracking isn't working, though.
That red area shows roughly where background objects still act as obstacles. Below that, they don't. The space below the red area, and including it, is outside the normal frame area; I make it visible by expanding the virtual height of the frame when the player drops out of the bottom of the frame.
you could possibly make the frame as large as the sprites, and set the camera Y to the middle of the frame so it doesnt go below.
if youre using a smaller resolution, you could problably just say when whatever the camera object is is below whatever ammount of pixels then set screen to it.