Issue mixing MP4s and PNGs

I'm trying to create a show that has a mix of PNGs and MP4s, with UDP commands to move between content.

When I cycle through the PNGs, they all display fine. I then get to an MP4, which plays correctly, and I move to the next PNG, which also displays correctly, but every other PNG in the presentation then fails to display, I just get a black screen. This includes PNGs which were working before the video played.

I know I'm still moving through the presentation, because I can send 'next' a number of times, and then can scroll back to the MP4 by sending 'back' the same number of times. It seems like the video engine is kicking off and stopping the PNGs from displaying correctly.