Unexpected Results by optimize_join_buffer_size

CREATE TABLE t0(c0 CHAR(100));

CREATE TABLE t1(c0 CHAR(100));

INSERT INTO t1 VALUES ('\r');

INSERT INTO t0 VALUES ('');

INSERT INTO t1 VALUES ('');

SET SESSION join_buffer_size = 6503032224856747123;

INSERT INTO t0 VALUES ('a');

SELECT t0.c0 FROM t0 INNER JOIN t1 ON (t1.c0 REGEXP t1.c0); -- {}, {'a'}

SET STATEMENT optimizer_switch = 'optimize_join_buffer_size=off' FOR SELECT t0.c0 FROM t0 INNER JOIN t1 ON (t1.c0 REGEXP t1.c0); -- {}, {'a'}, {'a'}