Странный скачок времени

sergey@debian:~/dev/tzdata$ cat test.c
#include <time.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
        struct tm localTM;
        time_t t1, t2;

        localTM.tm_sec = 0;
        localTM.tm_min = 0;
        localTM.tm_hour = 0;
        localTM.tm_mday = 7;
        localTM.tm_mon = 0;
        localTM.tm_year = 109;

        t1 = mktime(&localTM);

        localTM.tm_mday = 6;
        localTM.tm_hour = 23;
        t2 = mktime(&localTM);

        printf("t1 == t2: %d\n", t1 == t2);

        return 0;
}
sergey@debian:~/dev/tzdata$ gcc -o test test.c
sergey@debian:~/dev/tzdata$ ./test
t1 == t2: 1
sergey@debian:~/dev/tzdata$ date +%Z
MSK