Are you changing your local information between executions or between rebuilds of the executable?

I believe there is a "C" locale specifically for reasons like this (ensuring the compile/build process is predictable), but if you're getting different results between executions of the app, depending on your locale settings, I'd be tempted to wonder if this were a bug as you suggest.

Unfortunately, I'm no embedded C expert, nor am I a locale expert. Perhaps someone else can give more information.