| There is a little sensor at the back of the handbrake under the cover that is triggered when the hand brake is up. If the connector comes loose then it can play up at the different times when it doesnt need to.
Check the operation of the sensor when stationary by taking then hand brake on and off a few times. if it responds without a problem then all is probably fine. if the problem persists then remove the handbrake cover and check the connection of the sensor.
Alternatively if you want a free car wash take it to the dealer (if it is under warranty) and get them to do all the work for you.
Andrey | 
