Premiere scaled image hides lower layers
I frequently place a "slide" (an 80% resized .png file) over background images/video.

In the timeline it looks like this:

Frequently, it blocks lower layers in Premiere program monitor, but it will render fine. There is no masking here.

If I disable/enable the image items (individually) on the timeline, this ususally fixes the problem. But then when I reeopen Premiere for a later edit, the lower layers are again hidden. Problem occurs with JPG or PNG imaages. Haven't really tried with other formats.
It's especially painful with 100+ "slides!"
Any ideas on why this is happening/how to cure?
Thanks!