I was able to show a reproducible error. I created a new project and added a light pink background on V1. I added a photo on V2 sized to show the pink background. I made the photo 3 seconds long to show the effect more clearly. I grabbed the Throbber to extend the fade duration and you can plainly see the error occur - every time. There may be other conditions where this will show up - but this one is consistent. Note that muting the pink background track V1 this anomaly is not revealed.
-=Ken=-