You may wish to turn on run-time checking (-C for the newer Intel compilers) along with the debug option, and see if the problem becomes more visible. Try first without optimization, then repeat with the optimization you intend to use. The default optimization (e.g. -O2), which Intel compilers use in the absence of the debug option, is reset to a lower level by the debug option, unless you specify it.
In the debugger of your choice, you should be able to set a watch breakpoint on the variable of concern, once you have fixed any basic problems.
