Quicktime Broadcaster sometimes only records audio

[jb60606]

Sometimes, Quicktime Broadcaster won't record video to file -- only audio. There's a video feed present in the preview window... it just doesn't show up in the file. Sometimes, starting the recording again or restarting QB helps -- other times it doesn't.

Does anyone else have this problem?

Mac Pro (February)
Octo 2.8Ghz
8800GT
8GB
750GB Samsung (OS drive, so it's already spinning when the recording starts)
iSight Camera on Kaidan mini-tripod and Kenko wide angle lens.

Thanks in advance.