LP:314570 - update is not changing internal auto increment value

create table t1 (a int not null auto_increment primary key, val int);
insert into t1 (val) values (1);
update t1 set a=2 where a=1;
insert into t1 (val) values (1);

leads to:

drizzletest: At line 307: query 'insert into t1 (val) values (1)' failed: 1062: Duplicate entry '2' for key 'PRIMARY'

For InnDB this fails, for MyISAM, it passes as MyISAM updates the auto increment value.