https://bugs.freedesktop.org/show_bug.cgi?id=29726
--- Comment #6 from James Le Cuirot chewi@aura-online.co.uk 2010-10-24 16:03:20 PDT --- I was thinking you actually meant the .drirc setting rather than an actual environment variable but you were right. Setting this in .drirc makes no difference but the environment variable does indeed make the problem go away.
I quite like vsyncing so I'm a little sad if it's broken. I think it was working before?