Query:

SELECT a
FROM t1
WHERE a = (
SELECT t2.a
FROM t2
) OR t1.a = 73
GROUP BY 1;

backtrace:

#3 0x082987db in handle_segfault (sig=11) at mysqld.cc:2810
#4 <signal handler called>
#5 0x08348964 in add_ref_to_table_cond (thd=0xa2c56e0, join_tab=0xae630f00) at sql_select.cc:19919
#6 0x0831dcb6 in JOIN::optimize (this=0xae6269f0) at sql_select.cc:1543
#7 0x08322209 in mysql_select (thd=0xa2c56e0, rref_pointer_array=0xa2c725c, tables=0xae613078, wild_num=0, fields=..., conds=0xae613f58, og_num=1,
order=0x0, group=0xae614078, having=0x0, proc_param=0x0, select_options=2147764736, result=0xae614118, unit=0xa2c6e40, select_lex=0xa2c7120)
at sql_select.cc:2886
#8 0x0831a05f in handle_select (thd=0xa2c56e0, lex=0xa2c6de4, result=0xae614118, setup_tables_done_option=0) at sql_select.cc:283
#9 0x082b482c in execute_sqlcom_select (thd=0xa2c56e0, all_tables=0xae613078) at sql_parse.cc:5112
#10 0x082ab5e9 in mysql_execute_command (thd=0xa2c56e0) at sql_parse.cc:2250
#11 0x082b6e5b in mysql_parse (thd=0xa2c56e0, rawbuf=0xae612ec0 "SELECT a\nFROM t1\nWHERE a = (\nSELECT t2.a\nFROM t2\n) OR t1.a = 73\nGROUP BY 1",
length=74, found_semicolon=0xae9e1228) at sql_parse.cc:6112
#12 0x082a9238 in dispatch_command (command=COM_QUERY, thd=0xa2c56e0,
packet=0xa31e321 "SELECT a\nFROM t1\nWHERE a = (\nSELECT t2.a\nFROM t2\n) OR t1.a = 73\nGROUP BY 1", packet_length=74) at sql_parse.cc:1221
#13 0x082a8693 in do_command (thd=0xa2c56e0) at sql_parse.cc:916
#14 0x082a5677 in handle_one_connection (arg=0xa2c56e0) at sql_connect.cc:1191
#15 0x00821919 in start_thread () from /lib/libpthread.so.0
#16 0x0076acce in clone () from /lib/libc.so.6

explain also crashes:

reproducible with default switches. reproducible on maria 5.3. not reproducible on maria-5.2, mysql-5.5

bzr version-info
revision-id: <email address hidden>
date: 2011-10-12 02:04:03 +0400
build-date: 2011-10-12 10:25:51 +0300
revno: 3224
branch-nick: maria-5.3

test case:

CREATE TABLE t1 (a int, PRIMARY KEY (a)) ;
INSERT INTO t1 VALUES (14),(15),(16),(17),(18),(19),(20);

CREATE TABLE t2 (a int) ;

SELECT a
FROM t1
WHERE a = (
SELECT t2.a
FROM t2
) OR t1.a = 73
GROUP BY 1;