Compiling Fortran for debugging

I use pgf90 7.1 on a linux-64 machine. I want to debug an application developed in C++ mixed with Fortran. I can step into the fortran code in a debugger but sometimes, the highlighted line in the fortran code in the debugger jumps up and down, sounds like the fortran code has been compiled with some kind of optimization. But I compiled the code with “-g” (and even “-g -O0”) to pgf90. What could be the cause?

If I use “-Minfo” compiler flag, I can see the following messages:

1031, sum reduction inlined
1043, sum reduction inlined
1075, sum reduction inlined
1083, sum reduction inlined

Could this be the reason? If yes, how to compile the code which will be good for debugging?

By the way, here are the flags I used:
/opt/pgi/linux86-64/7.1/bin/pgf90 -Mextend -Mfixed -Minfo -Mrecursive -O0 -D__linux -Dlinux_64 -Dlinux_64_s92 -Dlinux -I. -I… -DNO_CG_AUTO_PTR -DVSL_LINUX -DSYSTEMV -DVSL_LP64-DNEW_CPP_EXCEPTIONS -DVSL_IX86ENDIAN -g -c mysrc.f -o mysrc.o

Any comments will be appreciated.