Steve, one additional point. In addition to removing those folders after each use I also need to restart the program. Otherwise, when I add new files the timeline loads with the prior clips that were deleted.
Jim
Will assume there is no definite resolution to this issue so this will be my final comment and will mark as complete. The problem does not occur with files captured on my digital camcorder and downloaded to computer. The issue originated with old movies copied from VHS or Mini VHS tapes to DVD and subsequently downloaded to computer from DVD to save as MP4's. Hope this helps in your future research to possibly ultimately determine the cause.
Thanks for all your help.
Jim