MovieMaker – Saved Movie is Different Than Project Movie

I trim the beginning and end off my MP4 file. Then, I edit out a small section in the middle. When I play it back in MovieMaker, the edit in the middle is exactly how I want it. But when I save the movie, and replay it, the edit in the middle is not correct. It's missing about a second that is supposed to be there, so the result is a person's sentence getting cut-off before the last word. Why is this happening? I've tried making this work over and over again, changing the way I am editing the middle section each time (trim, split, delete, etc., etc.) Nothing works. Makes no sense. It plays one way as a "project" and another way as the saved movie file. Except for that middle section, everthing else replays exactly as I edited it.