PERFECTLY NORMAL
When the scoot is cold, the auto-choke is keeping the revs up in the engine, since the engine revs are up, the belt is moving fast enough to make the clutch, that is attached to the rear of the bike, engage and make the wheel spin. When the bike warms, the auto-choke will let off , the revs will go down, the clutch will release and the wheel will stop free wheeling.
Before I go for a ride, I start my scoot on the center stand as one of the first things I do. Then I gear with the jacket, helmet, gloves... When the revs drop and wheel stops spinning, I am ready to go. Some debate the need to warm the bike to get the oils and such moving. I don't worry about that, I know that my bike will run smoother, accelerate better, not stall at lights, and not want to creep out from under me while waiting for the green light.
So.. I warm my bike every ride. It takes about the same time as gearing up, 2-3 minutes at most.