The query with -ps-protocol crashes the rserver because select>prep_where references on freed memory (it was Item_outer_ref):

CREATE TABLE `t1` (
`pk` int(11) NOT NULL AUTO_INCREMENT,
`col_varchar_key` varchar(1) DEFAULT NULL,
PRIMARY KEY (`pk`),
KEY `col_varchar_key` (`col_varchar_key`)
) DEFAULT CHARSET=latin1;
INSERT INTO `t1` VALUES (10,'v');
INSERT INTO `t1` VALUES (11,'r');
CREATE TABLE `t2` (
`pk` int(11) NOT NULL AUTO_INCREMENT,
`col_varchar_key` varchar(1) DEFAULT NULL,
PRIMARY KEY (`pk`),
KEY `col_varchar_key` (`col_varchar_key`)
) DEFAULT CHARSET=latin1;
INSERT INTO `t2` VALUES (1,'r');
INSERT INTO `t2` VALUES (2,'c');
CREATE TABLE `t3` (
`pk` int(11) NOT NULL AUTO_INCREMENT,
`col_varchar_key` varchar(1) DEFAULT NULL,
PRIMARY KEY (`pk`),
KEY `col_varchar_key` (`col_varchar_key`)
) DEFAULT CHARSET=latin1;
INSERT INTO `t3` VALUES (1,'w');

SELECT SUM( DISTINCT table2 . `pk` ) AS field2 ,
(SELECT SUM( SUBQUERY1_t2 . `pk` ) AS SUBQUERY1_field1
FROM t2 AS SUBQUERY1_t2 STRAIGHT_JOIN
t3 AS SUBQUERY1_t3 ON (SUBQUERY1_t3 . `pk` = SUBQUERY1_t2 . `pk` )
WHERE table1 . `col_varchar_key` ) AS field3
FROM ( t1 AS table1 LEFT JOIN
( t2 AS table2 STRAIGHT_JOIN
t3 AS table3 ON (table3 . `pk` = table2 . `pk` ) )
ON (table3 . `col_varchar_key` = table1 . `col_varchar_key` ) )
WHERE ( table1 . `pk` < 5 ) OR ( table1 . `col_varchar_key` IS NOT NULL)
GROUP BY field3
HAVING (field3 <= 'h' AND field2 != 4) ;
drop tables t1, t2, t3;