Shape Mask and Transition

I need to block the name of a person from a slide that I've put in during a lecture video. I used the shape mask & blacked out the name. All good so far.

But when I put in a cross fade transition on either end of the slide (which I'm using for all the slides or still shots in the video) the name is visible for a moment at the beginning and end end of the transition.

How can I black it out entirely without this little glitch?

Thank you

Steve