imovie: mp4 codec makes a bouncing glitch

[iPowers]

For some strange reason, when you export a movie using the mp4 codec, when there are darker images in the video,s it seems to make some sort of blury bounce, like something wants to pop out the video.

This example could help a little.

http://www.youtube.com/watch?v=8l1aW06ldCI

Look at my other vids for other examples and see the darker parts of this one, or any other one.