From the Dec 2011 MQX-uVision getting started guide:
6.20 ARM MDK Keil uVision Support – Optimization in Release target MQX libraries
The code optimization level in the ARM MDK Keil uVision Release target is reduced to 0. Sporadic application crashes were observed in case any higher optimization level was used. The root cause of the issue was not known at the release date.
This seems like a major issue. Has this been resolved? I contacted Keil but they know nothing about it.