Updating user profile results in error message

Hi, I've updated half of my Drupal sites to v6.17 (from v6.16), and noticed in one of them that when I updated my user profile, I received this error:

warning: preg_match() [function.preg-match]: Compilation failed: range out of order in character class at offset 10 in /var/www/vhosts/mysite.com/httpdocs/modules/user/user.module on line 393.

I've checked on all my recently updated v6.17 sites, and it occurs on all of them. You don't need to change any of your details either, just go edit user and click save and the error above occurs.

I did a quick check on all my v6.16 sites, and the error does not occur.