I created a movie maker project and found out that when playing the movie not from the begining there was serious Sync problem between audio and video . Audio had a few seconds of delay.

I was breaking my head trying to understand why and eventually found that in ONLY HAPPENS IF THE AUDIO IS MP3.

Once I replaced the audio with a WAV file , everything works well.

Please fix for the sake of mankind. Its absolutely impossible to work with Movie Maker if there is an AV sync delay like the one I had..