I am having a recurrent problem whereby the image that fades out in the "Picture in Picture" track will flash on the screen after the fadeout occurs. This "fadeout flash" does not happen in the working phase of the project, only in the "exported" phase of the project. It is not happening consistently and happens in videos of varying complexity and length. It also occurs in various exported formats. An example of this can be found here at 1:20: 

https://www.youtube.com/watch?v=T31B_h8FKOo&list=PLDcUYWfF15hlpQeFCsQD2a7tMDpRM6w2m&index=24

What is going on? How can this be fixed?