I would be surprised if it is a vent problem. More likely there is an electrical problem. If it quits in the rain, it will quit under a water hose. My 06 TBA has 22+kmiles on it with a considerable amount of time in heavy rain. Plus washing with high-pressure washers ie carwashes and being left uncovered in the rain. No water related issues to date. However, if I do have a problem in the future, I'll look at my kill switch on the throttle control, then the interlock switch on the kickstand, and finally the plugs on the wiring harness associated with the ignition system. Beyond that I'll have to get a schematic and get serious with the troubleshooting.
I use my bike for the commute too. It is important that functions rain or shine. Stay on your dealer till he makes it right.
If it is a vent problem, it should consistently occur within just a few miles of a fillup whether its raining or not. There is a system that is supposed to reclaim fuel that spills through the overflow/vent line that might malfunction or be affected by moisture. I don't know the proper name for it but if your bike has that, there will be a black cylinder shaped device with wires and tubes connected to it underneath the air box mounted to the bottom of the frame behind the engine. I suppose if that didn't work right it might duplicate the vent problem.
