Spurious ER_OUT_OF_SORTMEMORY (1038): Out of sort memory on SELECT

--source include/have_innodb.inc

CREATE TABLE t(c INT,c2 TEXT) ENGINE=InnoDB;

SET @@SESSION.sort_buffer_size=30839;  # up to 30839: error, 30840: no error

SELECT c,LAG(c,1) OVER w FROM t WINDOW w AS (PARTITION BY c2 ORDER BY c2);

DROP TABLE t;  # Cleanup

mysqltest: At line 12: query 'SELECT c,LAG(c,1) OVER w FROM t WINDOW w AS (PARTITION BY c2 ORDER BY c2)' failed: ER_OUT_OF_SORTMEMORY (1038): Out of sort memory, consider increasing server sort buffer size