Entering an invalid date (20111-02-03 in this case) into the "Find a member" search forms "joined" input element results in SQL query error (General Error) copied below.

General Error
SQL ERROR [ mysqli ]

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 4 [1064]

SQL

SELECT COUNT(u.user_id) AS total_users FROM phpbb_users u WHERE u.user_type IN (0, 3) AND u.user_regdate <

BACKTRACE

FILE: includes/db/mysqli.php
LINE: 163
CALL: dbal->sql_error()

FILE: memberlist.php
LINE: 1263
CALL: dbal_mysqli->sql_query()