Why oh Why? PSE14 trimmed clips will not stay trimmed..

Oh, I hope someone can help. My sanity is at stake here...

PSE14, Windows 10.

Expert mode. AVI files from my game camera. They import and play fine on the timeline and preview/clip monitor.

Problem: I need to trim the first four frames from each clip. No matter how I trim each clip, when I play the timeline the clips revert to untrimmed.

What I have tried: In preview/clip monitor I advance four frames and set the IN point. Right-click and select Insert to add pre-trimmed clip to timeline. On the timeline the clip appears to be trimmed. I repeat for remaining clips. When I play the timeline the clips are no longer trimmed.

I have also trimmed by dragging from the end of each clip on the timeline. All clips appear trimmed until I play the timeline and they are no longer trimmed.

I have also trimmed each clip on the timeline by advancing four frames and splitting, then deleting the unwanted four frames. Same story, all clips appear trimmed until I play the timeline and once again all clips are magically no longer trimmed.

If I can't solve this I fear I will go right off the deep end. Hopefully it is simple and someone can point me toward the light.

thanks,