Different EXPLAIN SELECT DISTINCT on just created table and after deleted records

create or replace table t1 ( id int not null, name varchar(20) not null, dept varchar(20) not null, age tinyint(3) unsigned not null, primary key (id), index (name,dept) ) engine=innodb;

explain select distinct t1.name, t1.dept from t1 where t1.name='rs5';

insert into t1(id, dept, age, name) values (3987, 'cs1', 10, 'rs1'), (3988, 'cs2', 20, 'rs1'), (3995, 'cs3', 10, 'rs2'), (3996, 'cs4', 20, 'rs2'), (4003, 'cs5', 10, 'rs3'), (4004, 'cs6', 20, 'rs3'), (4011, 'cs7', 10, 'rs4'), (4012, 'cs8', 20, 'rs4'), (4019, 'cs9', 10, 'rs5'), (4020, 'cs10', 20, 'rs5'),(4027, 'cs11', 10, 'rs6'),(4028, 'cs12', 20, 'rs6');

delete from t1;

explain select distinct t1.name, t1.dept from t1 where t1.name='rs5';

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

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

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

|    1 | SIMPLE      | t1    | ref  | name          | name | 22      | const | 1    | Using where; Using index |

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

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

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

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

|    1 | SIMPLE      | t1    | range | name          | name | 44      | NULL | 1    | Using where; Using index for group-by |

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

--- /home/midenok/src/mariadb/10.4/src/mysql-test/suite/innodb/r/innodb_mysql.result    2019-05-31 09:23:14.003022993 +0300

+++ /home/midenok/src/mariadb/10.4/src/mysql-test/suite/innodb/r/innodb_mysql.reject    2019-06-26 15:33:23.132090751 +0300

@@ -394,7 +394,7 @@

 # Masking (#) number in "rows" column of the following EXPLAIN output, as it may vary (bug#47746).

 EXPLAIN SELECT DISTINCT t1.name, t1.dept FROM t1 WHERE t1.name='rs5';

 id     select_type     table   type    possible_keys   key     key_len ref     rows    Extra

-1      SIMPLE  t1      range   name    name    44      NULL    #       Using where; Using index for group-by

+1      SIMPLE  t1      ref     name    name    22      const   #       Using where; Using index

 SELECT DISTINCT t1.name, t1.dept FROM t1 WHERE t1.name='rs5';

 name   dept

 DROP TABLE t1;