mex -g problem (Debugging) on Win7

When I compile my very simple function with the -g option for later debugging, the C function call sqrt() within my function is not returning a correct result. It is the same result if I put it in VS2010 debugger with the attach to process procedure, or call it the plainly from matlab. The very same code, when compiled without the -g option, runs correctly. It seems like libraries are not linking properly when -g is invoked. Do I need to put something special in the mexopts.bat?