Compilation failed: lookbehind assertion is not fixed length at offset 5

After upgrade to PHP 5.2.1, receive the following error when attempting to post:

[phpBB Debug] PHP Notice: in file /includes/message_parser.php on line 1200: preg_replace() [function.preg-replace]: Compilation failed: lookbehind assertion is not fixed length at offset 5

Warning: Cannot modify header information - headers already sent by (output started at /store/flygroup_v2/forum/includes/functions.php:3266) in /store/flygroup_v2/forum/includes/functions.php on line 3726

It appears that it is not accepted by PCRE (the library used by PHP to handle the regexes). And also that PHP isn't going to change it or fix it. http://bugs.php.net/bug.php?id=38327" target="_blank

FreeBSD 6.2-STABLE
Apache/1.3.37
PHP 5.2.1
MySQL 5.0.33
PHPBB 3.0.B6-dev