It's a limitation of the phpBB parser for URLs. Anything that is a character that a 3 year old child wouldn't recognise is treated as a special character and is not considered part of a legit URL.
I can only assume that said 3 year old child designed the URL parser.
At any rate, things like apostrophes, spaces, brackets etc etc all need to be manually escaped to their URL-friendly code.
So left bracket is ( and right is )
http://en.wikipedia.org/wiki/Warden_(software)
This will give you a pretty URL that looks the way it should. The disadvantage is that phpBB, in its infinite wisdom, will cheerfully convert them in the DB to the "naughty" characters it doesn't like. So if you quote or edit a post with those encoded chars, the URL will break again, unless you manually change them back to the URL-friendly code.
The alternative (makes for ugly URLs that always work) is to use % to encode the hex value (found
here for eg) of a character like so:
http://en.wikipedia.org/wiki/Warden_%28software%29
To de-uglify this horrid looking thing, use the [url] tags:
Haer iz teh lnik, do joo leik mudkipz?
This has been an unwelcome education.
The moar you know!
TLDR:
Use % and the
hex number of the character you want, stick it in url tags:
%20 = space
%28 = (
%29 = )
etc etc
Who do you think you are? If you'd stopped winning, you could have been the Biggest Loser, if you gave up, you could have been a Survivor, if you'd stopped reading Orwell, you could have been on Big Brother!