Thats an awesome question. I exported straight out of after effects (black was at 0) and into fcpx. Its just words…The end card its sitting on top of doesn’t even approach 0, but on the scope I see some small jaggy bits going under 0…
But its Interesting. If I take my main spot which has legal blacks, and add the broadcast filter to it, it does the same thing. lowers black into illegal territory.