Mask "shadow" showing up in the middle of the scene

Question

Ok, I've got a question which is pretty hard to explain.

I'm using Premiere Pro CC to produce a short movie.

Here's a picture describing (or at least trying to) my set:

"A" is the main track. "B" is the second track which I placed in the bottom right corner and "C" is an opacity mask on that track. On this track I've used Ultra Key to remove the background. I've also added a Cross Dissolve effect on "B".

So here's the problem. During the cross dissolve the mask ("C") shows in the middle of screen ("D").

Is this a bug or am I doing something wrong? How do I remove "D"?

Thanks!

Answer 1

During the time range in which the dissolve occurs, split the clip on A, place that segment on a track above B, and apply a mask on A so that C shows through. You can do this by creating a mask to show the C region and then invert it.