Can't remove a call_out.

Seems like a bug, I can't remove a call_out by function name right after
scheduling it.

void test()
{
    bool testvar = false;

    void do_timeout()
    {
        testvar = true;
    };

    void check_timeout()
    {
        mixed a = call_out( do_timeout, 20);
        werror("a: %O\n", a);
        werror("check_timeout(): %O\n", remove_call_out( do_timeout ));
        werror("check_timeout(): %O\n", remove_call_out( a ));
    };

    check_timeout();
}

int main(){
    call_out(test, 0);
    return -1;
}

I am able to remove it by the call out id returned from call_out. Also I am
able to remove the call out if I remove the testvar variable or move it
into the global scope.
So this works:

void test()
{

    void do_timeout()
    {
       werror("to\n");
    };

    void check_timeout()
    {
        mixed a = call_out( do_timeout, 20);
        werror("a: %O\n", a);
        werror("check_timeout(): %O\n", remove_call_out( do_timeout ));
        werror("check_timeout(): %O\n", remove_call_out( a ));
    };

    check_timeout();
}

int main(){
    call_out(test, 0);
    return -1;
}


Stefan