you may have the rain sensing wipers, which i personally don't like. i can turn them on myself. anyways...if you do, and if it's anything like what i used to have in a vehicle, when in that mode, they would wipe once when you turned the car on - kind of a 'check' to ensure they are working.
if you don't have the rain sensing wipers...may need a trip to the dealer for some diagnostics and warranty repair