Hi all. I have my 2008 C5 with a AM6 gearbox for 6 mounths now and it`s great i love it

but quite for a while now the auto gearbox have a strange behavior. The thing is that after i whait for a while at a trafic light in Drive when i lift the brake pedal the car moves as normal but immediatley the is a kick as the car gain speed without presing the gas pedal. If the waiting time in drive mode is lower (unde 6-7 second) the car drive off smoouth without any kick. So the box kicks only if i whait for a longer period in Drive. I tried to put in on neutral on the trafic light and when i put the gear lever in D from N it drive off smoothly with no kick.
I tried even in Reverse but it drives smoothly.
I need to mention that the kick is not hard, it`s just like when you lift the cluch pedal a bit fast on a manual box and it not make it all the time ! The gear changes are smooth as normal.
Is something wrong with the gear box or is just normal to be like this ? When wainting in D for a long time the box goes intro a auto N mode or something like that ?
Will a part oil change can do any beter ?
Thank you and please excuse my english
