Lexus: GS400 tire changing

I don't know if anyone has experienced this but, here goes. A couple years
ago I had a flat and was on a slight incline. With the car in park and the
parking brake set, it rolled back off the jack. A month ago, my wife called
and said she had a flat. The car again was on a slight incline. Again,
with the car in park and the brake set, I just got the lug nuts on a turn or
two, and the car rolled backward and came off the jack. This seems like a
serious saftey issue. I've never experiened this with any other car I've
owned , nor heard of it happening.
Any comments from the Lexus group?

I believe the parking brake only brakes the rear wheels. Likewise, putting
the car in park only locks the rear wheels on a RWD car. So if you're on an
incline and jack either front wheel without other measures, then it will be
suspectible to rolling off.

I don't know if the GS is more suspectible that most, but you should always
chock the wheel diagonally opposite the one you're changing.

- Mark