Animated movies have duplicated frames bug?

Has anyone noticed when creating an animated render (a video version of the 3d scene) that there are repeated frames inside the end result?

I stamped each frame with the frame number and had a slowly moving object in the video.

As I watched this I noticed a slight twitch and when stepping through frame by frame found that one or two frames had been repeated. The object didn’t move and the stamped frame number was identical.

This happened in 3 different renders of different parts of the entire animation.

This only happend with one or two frames in each sequence of say 200 frames. I had to re render the missing frames and cut out the repeated ones.

H264 8 bit color 100% v2.73 Windows7 pro 64bit