It's been pretty obvious that he has a problem with his left lat from 2006 on. What is causing this is anyone's guess.
He denies it anytime he is questioned on it.
Check out a recent lat spread from the rear in this video:
http://www.youtube.com/watch?v=rYXKSFeF5FA
It's obviously not getting any better either because this is posing exhibition from April 2008.