i think theres a "park" contact inside, which is probably gunked up or shorting out, that tells the wiper motor its finished its sweep, when you "spray" this park contact gets ignored and the motor just runs full time, however when you have it pushed back, its effectively on intermittant, and the park contact gets used every sweep to tell the motor when to stop.
Ours used to do that, and now it doesnt stop for ages, just keeps wiping away.
I've also noticed ours seems to be leaking, theres rust colored water over the back of the unit, is this a common issue?
Also 95-97 Avants have a different motor part number to the later cars, anyone know if its interchangable and what the differences are? The early one only seems to be fitted to A4's and seat arosas, the later one is used on all sorts of Audis and VW's