I warn anybody before using ARM Keil 4.13a. It generates defective code. I have spent several hours with debugging a code that has been already worked. The problem affects local variables of functions and passing arguments. Code has been wrongly compiled without any optimization. I have no courage and time to test optimizations.
I also encourage Keil not to publish Keil 4.13a any more.
Keil 4.12 seems to be OK.
But you will get better service from the garage if you can clearly demonstrate that it is due to a fault in the car, rather than your driving style!
I think you are confusing identifying a bug with fixing a bug.