Rear shock problem

My kid is having what I percieve as a problem with the rear shock. WE recently had the shock seal head replaced and the local suspension guy said he could adjust the piston for better flow to match the kids weight. I have noticed that since then the bike seems to be bouncing a lot more going in to corners. The bike is going side to side and up/down a bit more. Also the rear tends to come up on him a lot more now. This weekend he hit a jump he always hits smooth and clears and ended up on his face. The rear came up to the noon posistion and front was at 6. I do understand that he could have hit a kicker on the face but it seems weird to have these problems after the suspension work.
I did do a quick push down on the suspension and the rebound is faster than it used to be but it is definetly got some rebound damning there. Its not like the shock is blown. I didn't dink with the preload on the spring either. Its a non clicker type shock on a Cobra if it helps any. Only adjustment is pressure change on the resivor.

Thanks
I figured I'd ask before I blamed it on the suspension alone.