DELETE with descending MEMORY BTREE scan stops after one row despite LIMIT 5

DROP DATABASE IF EXISTS memory_delete;

CREATE DATABASE memory_delete;

USE memory_delete;

CREATE TABLE descending_rows (

  k INT NOT NULL,

  pad CHAR(20),

  INDEX idx_k USING BTREE (k)

) ENGINE=MEMORY;

INSERT INTO descending_rows

SELECT seq, LPAD(seq, 20, '0') FROM seq_1_to_20;

FLUSH STATUS;

DELETE FROM descending_rows FORCE INDEX (idx_k)

 ORDER BY k DESC LIMIT 5;

SELECT 'descending_affected_rows', ROW_COUNT();

SELECT VARIABLE_NAME, VARIABLE_VALUE

  FROM information_schema.SESSION_STATUS

 WHERE VARIABLE_NAME IN ('HANDLER_READ_LAST', 'HANDLER_READ_PREV')

 ORDER BY VARIABLE_NAME;

SELECT 'remaining', COUNT(*), MIN(k), MAX(k), SUM(k > 15)

  FROM descending_rows;

CREATE TABLE ascending_rows LIKE descending_rows;

INSERT INTO ascending_rows

SELECT seq, LPAD(seq, 20, '0') FROM seq_1_to_20;

DELETE FROM ascending_rows FORCE INDEX (idx_k)

 ORDER BY k ASC LIMIT 5;

SELECT 'ascending_affected_rows', ROW_COUNT();

SELECT 'ascending_remaining', COUNT(*), MIN(k), MAX(k), SUM(k <= 5)

  FROM ascending_rows;

DROP DATABASE memory_delete;

descending_affected_rows	1

HANDLER_READ_LAST	1

HANDLER_READ_PREV	1

remaining	19	1	19	4

ascending_affected_rows	5

ascending_remaining	15	6	20	0