I took a look at it, and its really weird, but I have experienced similar problems with my game. Where the touch suddenly loose connection to the mouse or what to call it, and it just stop responding to anything or does really weird things.
Unfortunately I haven't used touch that much, but it could look like there might be a bug with the car behaviour and touch when used together. I had to drop the car behaviour in my game, but that wouldn't work for you, that easy as in mine.
But I think you could make it by setting the X, angle and Y position of the tank it self, but it could be quite complicated compared to the car behaviour.
Also it seems that the tank hits an invisible wall and after that it just looses all control. However why it react to something that aint there is really weird. If you don't get any other feedback I would post it in the bug forum, because it looks really weird.
I even tried to pretty much disable everything that could be disabled and still it locks up.
Anyway that my best suggestion unfortunately.