Wrong result upon LIKE with geostd8_nopad collations and index

CREATE TABLE t (c char(32), KEY (c)) ENGINE=MyISAM collate geostd8_nopad_bin;

INSERT INTO t VALUES ('r'),('rock'),('rr');

SELECT c FROM t WHERE c LIKE 'r%';

# Cleanup

DROP TABLE t;

SELECT c FROM t WHERE c LIKE 'r%';

c

rock

rr

Same with geostd8_general_nopad_ci collation, but not, for example, with geostd8_general_ci.

Since it only happens with a key, I don't suppose it's a feature of these collations.

Reproducible on 10.5+ with MyISAM and Aria.
Not reproducible on 10.4.
Not reproducible with InnoDB.