SET col = IGNORE writes NULL in multi-table UPDATE

CREATE TABLE t1 (id INT) ENGINE=InnoDB;                                                                                                                                                                                                                   

CREATE TABLE t2 (id INT, v INT DEFAULT 7, w INT) ENGINE=InnoDB;                                                                                                                                                                                           

INSERT INTO t1 VALUES (1),(2);                                                                                                                                                                                                                            

INSERT INTO t2 (id,v) VALUES (1,10),(2,20),(3,30);                                                                                                                                                                                                        

EXPLAIN UPDATE t1, t2 SET t2.v = IGNORE, t2.w = t2.id + 5 WHERE t1.id=1;                                                                                                                                                                                  

id      select_type     table   type    possible_keys   key     key_len ref     rows    Extra                                                                                                                                                             

1       SIMPLE  t1      ALL     NULL    NULL    NULL    NULL    2       Using where                                                                                                                                                                       

1       SIMPLE  t2      ALL     NULL    NULL    NULL    NULL    3                                                                                                                                                                                         

UPDATE t1, t2 SET t2.v = IGNORE, t2.w = t2.id + 5 WHERE t1.id=1;                                                                                                                                                                                          

select * from t2;                                                                                                                                                                                                                                         

id      v       w                                                                                                                                                                                                                                         

1       NULL    6                                                                                                                                                                                                                                         

2       NULL    7                                                                                                                                                                                                                                         

3       NULL    8                                                                                                                                                                                                                                         

DROP TABLE t1, t2;