If someone was about to make a post giving the link of the forums that the post will be on (e.g. http://www.phpbb.com/community/), then the space between the word prior to that URL goes away, linking the word and the URL together.

For this example, I'll use the word "the".

Let's say I want to make a post in http://www.phpbb.com/community with the following:

Testing the www.phpbb.com/community/

Testing the http://www.phpbb.com/community/

Then I click Preview, this happens (http is applied to the first, and the space between the word "the" and "http" is now gone in the second:

Testing the http://www.phpbb.com/community/

Testing thehttp://www.phpbb.com/community/

Clicking preview one more time gives us this (now the spaces are gone in both examples):

Testing thehttp://www.phpbb.com/community/

Testing thehttp://www.phpbb.com/community/

If I click submit, that's what we get - a new URL that doesn't work.