Problems...
 

Has anyone else found a problem with some of the video downloads?

You only get a portion of the video and the rest is audio, and when you click to skip a bit, it skips to a random bit of the video.

Any clues on how to stop this?

Could be poorly encoded video. Could also be a codecs issue. Try playing them with this player & see if it's any better: VLC - (click on link) _ (choose nearest mirror site) which has in-built codecs.