My app Labo Car Designer has been released , It was build with 2014.2275.
Because the ITMS-9000 error, I had to update sdk to 2013.2306, and I meet the physic problem mentioned in this post again, I have no idea how to fix it.
In order to illustrate the problem clearly, I uploaded two vidoes.
video a: Build with 2014.2275
http://www.youtube.com/watch?v=WF7pN7PlII4
video b: Build with 2013.2306
http://www.youtube.com/watch?v=tUfZa9rYP_U
In video b, the car floating in the air, and not fall to the ground.
This problem occurs on both the simulator and real device(iPad).