First this is about the HC12 compiler, this was not mentioned in this thread.
AFAIK, this warning should occur for plain C code only when the common code optimization is enabled. So if it disapears with -Onf, then you have to be careful with the displayed values of locals even if they are on the stack, but the generated code is correct. If it does not disapear, then I would recomment to provide a reproducible case here.
Daniel