Robert,
I was not able to reproduce the problem. I tried building your example for both COFF and ELF models, and I was successful in reaching main without having to remove idle function from the code.
My guess from your screenshot is that it is hitting a breakpoint you are setting in HeapMem.c. Just to make sure, can you remove all the breakpoints and try again? SYS/BIOS has some initialization code which runs before main() function is called and in this case, HeapMem is being called to initialize heap and the breakpoint you had set in HeapMem is causing it stop before it reaches main.
Hope this helps.
Vikram