Bad results with join comparing case insensitive VARCHAR/ENUM/SET expression to a _bin ENUM column

CREATE TABLE t1 (a ENUM('a') CHARACTER SET latin1 PRIMARY KEY);

INSERT INTO t1 VALUES ('a');

CREATE TABLE t2 (a ENUM('a','A','b','B','c','C','d','D','e','E') CHARACTER SET latin1 COLLATE latin1_bin);

INSERT INTO t2 VALUES ('a'),('A');

-- without the following insert the bug doesn't show, was fixed in MDEV-6978

INSERT INTO t2 VALUES ('b'),('B'),('c'),('C'),('d'),('D'),('e'),('E');

ALTER TABLE t2 ADD PRIMARY KEY(a);

SELECT t1.a res FROM t1 JOIN t2 ON t1.a COLLATE latin1_swedish_ci=t2.a;

SELECT t1.a res FROM t1 LEFT JOIN t2 ON t1.a COLLATE latin1_swedish_ci=t2.a;

DROP TABLE IF EXISTS t1,t2;

SELECT t1.a res FROM t1 JOIN t2 ON t1.a COLLATE latin1_swedish_ci=t2.a;

res

a

SELECT t1.a res FROM t1 LEFT JOIN t2 ON t1.a COLLATE latin1_swedish_ci=t2.a;

res

a

SELECT t1.a res FROM t1 JOIN t2 ON t1.a COLLATE latin1_swedish_ci=t2.a;

res

a

a

SELECT t1.a res FROM t1 LEFT JOIN t2 ON t1.a COLLATE latin1_swedish_ci=t2.a;

res

a

a