Here's an example of two videos from the same channel.
This one downloads fine:
http://www.youtube.com/watch?v=sSwtnxQrEGw (it only has one audio track)
This one I can't download:
http://www.youtube.com/watch?v=OVzt2rsfMc0 (has 3 audio tracks)
The videos are region locked to some Asian country's so I've been using a proxy to watch/download them (specifically I've been using 1 from Indonesia and Malaysia)
That's got nothing to do with the problem tho as like I've said some download fine (single audio track) only videos with multiple audio tracks won't download.
Thanks