Hello again, I came across this yesterday and found a work around. I'm using stills that change over the timeline in synch with the audio, sort of a slide show type of approach. One still that I used had to be edited to correct some content. I deleted it from the timeline, edited it in a cad program and saved it with the same filename. Then I placed it back on the timeline and the correction was not in the image on the timeline. I opened the PNG file and the correction was there, deleted the existing one and dragged the edited one back on the timeline with the same result. The only way I could get it to retain the edited version was to delete the image, save the file and exit the program. Upon re-starting the program I was successful in placing the new image.
Ed