I had this same problem the two times I've played with my 09 SLG...
It usually chops or pinchs a ball first (I'm assuming because the bolt slips of off the sear before the ball makes it all the way down into the breach). I need to reset the bolt using the button on the back, and then it starts shooting bursts and going fully auto. Turning off the gun doesn't help, I have to turn off the air. I don't know if it is because it is colder, but last night I was playing indoors and it was at least 55 degrees. After the first time it happened, I cleaned and checked the entire gun and relubbed it being careful not to use too much. It worked for a few games and started happening again.
If this problem is affect by temperature, I think gun manufacturers located in warmer climates should put a bit more effort into testing them where it gets cold.
I don't know what to try next.