Ah good point. Yeah I tried this on my local instance and have the same issue.
It's because of the inbuilt rules I guess:
Place + in front of a word which must be found and - in front of a word which must not be found. Put a list of words separated by | into brackets if only one of the words must be found. Use * as a wildcard for partial matches.
Edit: just a cursory glance, I think perhaps around https://github.com/phpbb/phpbb/blob/68c ... l.php#L215
is where it's happening. I am a shocker with Regex though, so hopefully someone else knows the solution off the top of their head before you need to rely on my deconstructing those regular expressions