Preg_match_all bug in om core

I get this error:

Warning: preg_match_all() [function.preg-match-all]: Compilation failed: unrecognized character after (?< at offset 3 in om_body_classes() (line 30 of /www/DOMAIN/sites/all/themes/om/core/inc/om_utils.inc).

My settings:
* Drupal core 7.9
* PHP 5.2.17
* PHP extensions: Enabled
* PHP memory limit: 256M
* PHP register globals: Disabled
* Web server: Apache/2.2.3 (CentOS)

Best regards
Raf