Movie being doubled in length after initial processing

I've been using Movie Maker for over 2 years now without any problems.  For the last month whenever I add a video clip it will display the total time while going through the initial processing, but it will stall at 99% and when it's finally finished the total time of the video will now be doubled in length.  A 25 minute video will now be a 50 minute video with the last image repeated for those extra 25 minutes.  Why is it doing this and how can I make it stop.  I've been editing that extra time out but it's really starting to be pain.