I have experienced the same...car lunged forward after stopping foot on brake...my wife experienced it also this week freaked her out. I have 89.3K miles going to do throttle body and transmission drain and fill soon.

 

Many people probably did not realize GS and other Lexus cars would use engine drag to assist braking when brake is applied. When you slow down and stop from speed, the engine would cut fuel but transmission would remain engaged and shift through the gears until you have slowed down to a low speed where the computer would recover the fuel supply and re-ignite the engine. That's probably the moment you get a "lurch" sort of feel, usually at 1st or 2nd gear, where the engine switches from helping stop the car to driving the car.

If the car hasn't been fully warmed up and engine idles high rpm, the "lurch" would be more pronounced than otherwise.

This is speaking from experience and observation. I'm no GS expert. But the car is sure having no problem that way. I have long got to use to that behavior and stopped paying attention to it anymore. The engine has no way of out powering the brakes so we are safe. Just keep the brakes checked up every year and hydraulic system flushed every other years.

BTW, transmission fluid drain-n-fill may help depending on age/mileage of the fluid. I did a 12 Qt drain-n-fill at 100K miles and the lurch seemed to have eased a bit, along with a slightly improved shift feel in general.