Good question really, and reading though the responses, it sems that this bike is prone to doing this.
I stall sometimes too. I ride the bike VERY gently in traffic, and i've given her a -2 back sprocket, and idle is low too.
Practicing is the key, just getting used to it. Parking lots are your friend, especially ones with an incline somewhere.
When you stall in traffic, the key is keeping calm, and restarting immediately, but that's just a practice thing too. :thumbup: