Having trouble with the Internal Media Frame (IMF) not clearing. So running the IMF controls to full (255), letting it take its time, then setting it back to (0) and also letting it take it's time, usually clears the frost.
Doesn't always work though.
So, last time I tried this and it didn't work I added an element. I first zoomed the fixtures out wide (100%), then ran the IMF to full, then ran the IMF out. That worked even after I had tried the regular IMF FULL>OUT trick several times with no success.