Unexpected index intersection with full index scan for an index

CREATE TABLE t1 (

  id int(10) unsigned NOT NULL AUTO_INCREMENT,

  p char(32) DEFAULT NULL,

  es tinyint(3) unsigned NOT NULL DEFAULT 0,

  er tinyint(3) unsigned NOT NULL DEFAULT 0,

  x mediumint(8) unsigned NOT NULL DEFAULT 0,

  PRIMARY KEY (id),

  INDEX es (es),

  INDEX x (x),

  INDEX er (er,x),

  INDEX p (p)

) ENGINE=InnoDB DEFAULT CHARSET=latin1;

insert into t1(es,er) select 0, 1 from seq_1_to_45;

insert into t1(es,er) select 0, 2 from seq_1_to_49;

insert into t1(es,er) select 0, 3 from seq_1_to_951;

insert into t1(es,er) select 0, 3 from seq_1_to_1054;

insert into t1(es,er) select 0, 6 from seq_1_to_25;

insert into t1(es,er) select 0, 11 from seq_1_to_1;

insert into t1(es,er) select 1, 1 from seq_1_to_45;

insert into t1(es,er) select 1, 2 from seq_1_to_16;

insert into t1(es,er) select 1, 3 from seq_1_to_511;

insert into t1(es,er) select 1, 4 from seq_1_to_687;

insert into t1(es,er) select 1, 6 from seq_1_to_50;

insert into t1(es,er) select 1, 7 from seq_1_to_4;

insert into t1(es,er) select 1, 11 from seq_1_to_1;

insert into t1(es,er) select 2, 1 from seq_1_to_82;

insert into t1(es,er) select 2, 2 from seq_1_to_82;

insert into t1(es,er) select 2, 3 from seq_1_to_1626;

insert into t1(es,er) select 2, 4 from seq_1_to_977;

insert into t1(es,er) select 2, 6 from seq_1_to_33;

insert into t1(es,er) select 2, 11 from seq_1_to_1;

insert into t1(es,er) select 3, 1 from seq_1_to_245;

insert into t1(es,er) select 3, 2 from seq_1_to_81;

insert into t1(es,er) select 3, 3 from seq_1_to_852;

insert into t1(es,er) select 3, 4 from seq_1_to_2243;

insert into t1(es,er) select 3, 6 from seq_1_to_44;

insert into t1(es,er) select 3, 11 from seq_1_to_1;

insert into t1(es,er) select 4, 1 from seq_1_to_91;

insert into t1(es,er) select 4, 2 from seq_1_to_83;

insert into t1(es,er) select 4, 3 from seq_1_to_297;

insert into t1(es,er) select 4, 4 from seq_1_to_2456;

insert into t1(es,er) select 4, 6 from seq_1_to_19;

insert into t1(es,er) select 4, 11 from seq_1_to_1;

update t1 set p='foobar';

update t1 set x=0;

SELECT * FROM t1

  WHERE ((p = 'foo' AND er != 4) OR er = 4 ) AND (es >= 4) LIMIT 2;

EXPLAIN EXTENDED SELECT * FROM t1 WHERE ((p = 'foo' AND er != 4) OR er = 4 ) AND (es >= 4) limit 2;

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

| id   | select_type | table | type        | possible_keys | key   | key_len | ref  | rows | filtered | Extra                                    |

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

|    1 | SIMPLE      | t1    | index_merge | es,er,p       | er,es | 0,1     | NULL | 1852 |   100.00 | Using sort_intersect(er,es); Using where |

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