Using the reset button (usually mapped to "r" key in the game) at speed while turning and perhaps about to hit a wall results in the car continuing to move after being reset. If the car is moving very fast when reset it will bounce violently when hitting the ground after resetting and sometimes flip high into the air. Could trimming also be used here to make sure the car is at rest before starting again?
This is not as bad when the hinges are correct, but it still occasionally happens - when turning hard or sliding fast, if I "reset car" it spins around after resetting. This only happens sometimes, but I could possibly make a replay of it.
make sure your reset car key/button is set to "held"
If I set my joystick reset button to "held", the simulation slows to a crawl - it only seems to update every half second or so. Removing the entry for the key "r" doesn't help this any. Setting it back to "once" makes everything fine again. I'm using the latest SVN code (of course).
Oh, right... yeah, binding a joystick button to reset and making it held doesn't work well. Setting the keyboard button to reset and held works the best, though.