mktime bug?

#include <time.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char* printtm(struct tm tm)
{
  static char buf[100];
  sprintf(buf, "%04d-%02d-%02d %02d:%02d:%02d (off=%ld, dst=%d)",
    tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
    tm.tm_hour, tm.tm_min, tm.tm_sec,
    tm.tm_gmtoff, tm.tm_isdst);
  return buf;
}

void test(int y, int m, int d, int hh, int mm, int ss, int isdst)
{
  // Prepare tm structs
  struct tm tm, tm2;
  memset(&tm, 0, sizeof(tm));
  memset(&tm2, 0, sizeof(tm));
  tm.tm_year = y - 1900;
  tm.tm_mon = m - 1;
  tm.tm_mday = d;
  tm.tm_hour = hh;
  tm.tm_min = mm;
  tm.tm_sec = ss;
  tm.tm_isdst = isdst;
  // Convert tm -> t -> tm and print
  printf("%s -> ", printtm(tm));
  time_t t = mktime(&tm);
  printf("%s -> ", printtm(tm));
  printf("%12ld -> ", t);
  localtime_r(&t, &tm2);
  printf("%s\n", printtm(tm));
}

int main()
{
  setenv("TZ", ":America/Los_Angeles", 1);
  tzset();

  test(2013,07,01, 12,0,0, 1);
  test(2013,01,01, 12,0,0, 1);
  test(1927,01,01, 12,0,0, 1);
  test(1929,01,01, 12,0,0, 1);
  test(1932,01,01, 12,0,0, 1);
  test(1934,01,01, 12,0,0, 1);
  return 0;
}