And I thought I was the only one with such problems.
The handbrake on my 156 has the bad habits of either not engaging (particularly in cold weather) or disengaging (in any weather). Hence I always park it in gear.
But one funny story (given that I lived to tell it) happened to me a few months ago. Got back home from a, erm, spirited drive, so I said I'll park with the engine on to let the turbo cool down for a few minutes. Now my parking spot is on a veeeery slight incline, then comes a fence, then a steeper incline and the house. Anyway, I parked the car, engine on, handbrake on and got off to take an admiration walk around it. As I was passing the front of the car (that meaning I was between the 1.6 ton monster and the fence) I heard a "bang" and noticed a slightly worrying tendency of the car to roll forward and turn me into a nice poster on the fence. I managed to recover in time to start pushing the car back, working my way bit by bit from the front passenger corner (where I had been standing when the handbrake let go) to the driver corner (of course, the only door open was the driver's) and then doing a heroic run & jump until I got into the seat, firmly pressed my foot on the brake, pulled the handbrake back, turned off the engine and put it into gear.
That said, I still love her, even if she tried to kill me.