I have a satisfactory explosion on a building and decided to throw in the canned falling debris effect. But the debris needs to fall behind some forground objects.
So I put the explosion elements and falling debris in their own composite shot so that I could add the composite shot back in and add a mask for the debris to fall behind. The mask works as expected when previewing in HF. However, when I render it out (I know it's called "export" in HF) my mask is not applied in the final render.