I spoke to Jay Cutler in person about 2-3 months before the 2006 Olympia. I told him that there were rumors online that Coleman had torn his tricep leading up to the show. Jay told me that was not the case. Jay said that Ronnie was suffering from bad tricep tendinitis, and it was interfering with his training (Jay ended up winning that show)
I wonder if the same thing was happening with his lat too. I believe that he gradually developed that asymmetrical lat issue. I think that it was noticeable in 2005. It got worse in 2006. And it was a glaring problem in 2007.
I know the answer to this, actually. It's an interesting story:
When Ronnie won his predictable #8 Sandow at the 2005 Mr. Olympia contest, he did his "shock and awe" victory collapse, where he fell on the floor in sheer awe of winning, like it took Sherlock Holmes to figure that out.

He damaged his elbow in that victory collapse - bursitis, as confirmed by e-mail, and posted on the MuscleMayhem website [a screenshot was posted].
That bursitis was evident as early as Ronnie's "On the Road" DVD by GMV Australia [Gallasch Muscle Video].
That bursitis affected Ronnie's complete training, and caused his left side to look atrophied, when he came back in 2006 at 290-lb [he was 275-lb in 2005, because the IFBB sent a mandate to Mr. Olympia qualified IFBB pros and said they should come down in size by X%, which caused Markus Ruhl to come in way off, and resulted in Ronnie coming in looking way differently, @275-lb].
Fast forward to the 2006 Mr. Olympia contest, and Ronnie was around 290, but his entire left side looked a wee bit off. Not WAY off...it wasn't until 2007 that you could REALLY see that [I believe the red trunks picture posted by joswift was 2007].
So...that's what happened. Ronnie injured his left triceps from his victory collapse in 2005. WINNING the 2005 Mr. Olympia is what caused him to LOSE the following year's Olympia. But hey - he was 41 in 2005, and injuries like that happen. UFC fighter Daniel Cormier stated that he hurt his back from SNEEZING. I guess that can happen with age.