[loki_the_glt]

I made a similar mistake many, many years ago when re-commissioning my uncle's FIAT 131 Mirafiori automatic. In that instance the inhibitor switch had stuck in the "off" (i.e. does NOT do what it says on the tin!) and the car shot backwards into the garage door. (The car had been left outside as the "garage" was their utility room-cum-storage space.)
Lesson learned, my dad and I put a set of axle stands under the back axle before attempting any further work involving engine/transmission.
Oh, and we hastily wiped the garage door and back bumper down. What my uncle didn't know, wouldn't give him a heart attack.