Again, if you use FRAPS and the frame rate counter falls below 30, then you are going to have stutters in the film. It is not a bug, It simply means your computer does not have enough resources to be able to use FRAPS to make a film from that AHF.
It really is easy to see why. If the video frame rate falls below 30FPS, then FRAPS simply duplicates frame data, which causes stutters in the recorded film.
It boils down to your computer's performance and resources available.