Ah sorry,I miss understood that one!
I would say that the self park switch in the wiper motor is in the huff there, but I've not replaced a Transit one. What happens is, the motor remains live even when switched off at the stalk, until the self park limit switch within the motor senses that the blades have parked. A replacement motor is usually the way forward, but lets here what the others say!
I'd check the wiper fuse that goes to the stalk switch. I think the stalk switch give the power to get the motor going, then it keeps going from an independent power supply regardless of the position of the stalk switch. So that it only parks at the bottom.
Will it start as it should in the fast speed?
2 Stalk Switch (play with it) with ignition on
3 Bad dirty connections
4 Motor assembly