[plt-scheme] scheme_warning in Embedded MzScheme

In my C program that embedding MzScheme, calling "scheme_warning" doesn't has any effects.

I do set scheme_make_stdout/scheme_make_stderr/scheme_make_stdin in my program. They all work fine if I use them by calling scheme_eval/scheme_eval_string. I also checked the source code of "scheme_warning", which should output to the stderr port. But if I call "scheme_warning" directly in C, the function just returns without any effect.

Would anyone (Matthew?) please explain? Or if it is a feature (although it doesn't sees natural to me), because everything are in C, I can call the C function that implements the port insteady of "scheme_warning".

Cheers,
Chongkai