Some other vault issues are: If you're vaulting the character crouches first, then vaults over the fence and crouches again, even if you were standing straight before vaulting. Very annoying if running away.
If your running and then vaulting over a fence, your character often slows down and swings one leg after the other iver the fence instead of jumping over it. Again, very annoying if running away.
(talking no in every situation about fences, but all those situations are true for everything that's vaultable)