mruby Bug? mruby cannot output int variables by mrb_define_method.

mruby_int_bug.c

/*
gcc -I mruby/include -I mruby/src -O3 -g -Wall -Werror-implicit-function-declaration mruby_int_bug.c -lm mruby/mrblib/mrblib.o -lm mruby/lib/libmruby.a
*/

#include <string.h>
#include "mruby.h"
#include "mruby/proc.h"
#include "mruby/compile.h"

mrb_value mrb_num_get(mrb_state *mrb, mrb_value str)
{
    return mrb_fixnum_value(100);
}

mrb_value mrb_st_get(mrb_state *mrb, mrb_value str)
{
    return mrb_str_new(mrb, "hoge", strlen("hoge"));
}

int main() {
    int n;
    mrb_state* mrb;
    struct mrb_parser_state* p;
    struct RClass *class;
    struct RClass *class_int;

    mrb = mrb_open();

    class = mrb_define_module(mrb, "Bug");
    class_int = mrb_define_class_under(mrb, class, "Check", mrb->object_class);
    mrb_define_method(mrb, class_int, "int", mrb_num_get, ARGS_NONE());
    mrb_define_method(mrb, class_int, "st", mrb_st_get, ARGS_NONE());

    char* code =
"require 'Bug'                     \n"
"t = Bug::Check.new()              \n"
"puts('-------------------')       \n"
"puts('aaa ' + t.st)               \n"
//"p('aaa ' + t.int)               \n"
"p(t.int)                          \n"
"p('bbb ' + t.st)                  \n"
"puts('-------------------')       \n";

    p = mrb_parse_string(mrb, code);
    n = mrb_generate_code(mrb, p->tree);
    mrb_pool_close(p->pool);
    mrb_run(mrb, mrb_proc_new(mrb, mrb->irep[n]), mrb_nil_value());

    return 0;
}