I set a drop shadow on a video track in V20. Left the project and when opened the next day, I could not alter the shadow. The numbers (intensity, blur, etc) were all at defaults but the shadow was where I set it and nothing would change it. I ended up deleting the video track and inserting a new one. There was only one event on the track so was not a big deal to redo in my case.

This is on a 1920 x 1080 progressive video project.