MIN(timestamp_column) returns a wrong result in a GROUP BY query

SET time_zone='Europe/Moscow';

CREATE OR REPLACE TABLE t1 (i INT, d TIMESTAMP);

SET timestamp=1288477526  /* this is summer time */ ;

INSERT INTO t1 VALUES (3,NULL);

SET timestamp=1288477526+3599 /* this is winter time*/ ;

INSERT INTO t1 VALUES (3,NULL);

SELECT i, d, UNIX_TIMESTAMP(d) FROM t1 ORDER BY d;

+------+---------------------+-------------------+

| i    | d                   | UNIX_TIMESTAMP(d) |

+------+---------------------+-------------------+

|    3 | 2010-10-31 02:25:26 |        1288477526 |

|    3 | 2010-10-31 02:25:25 |        1288481125 |

+------+---------------------+-------------------+

SELECT i, MIN(d) FROM t1 GROUP BY i;

+------+---------------------+

| i    | MIN(d)              |

+------+---------------------+

|    3 | 2010-10-31 02:25:25 |

+------+---------------------+

void Item_sum_hybrid::update_field()

{

  DBUG_ENTER("Item_sum_hybrid::update_field");

  Item *UNINIT_VAR(tmp_item);

  if (unlikely(direct_added))

  {

    tmp_item= args[0];

    args[0]= direct_item;

  }

  switch (result_type()) {

  case STRING_RESULT:

    min_max_update_str_field();

    break;

  case INT_RESULT:

    min_max_update_int_field();

    break;

  case DECIMAL_RESULT:

    min_max_update_decimal_field();

    break;

  default:

    min_max_update_real_field();

  }

  if (unlikely(direct_added))

  {

    direct_added= FALSE;

    args[0]= tmp_item;

  }

  DBUG_VOID_RETURN;

}