I found a slight bug with the official phpBB.com forums. I DON'T have the time to get a working phpBB3 board and test it on my own so I can't test whether this is a bug with vanilla phpBB3 RC5 boards or not.....

Anyways, look at the first post of this thread:
http://www.phpbb.com/community/viewtopic.php?f=70&t=544491&start=0

Notice how the [!http://img70.imageshack.us/img70/4044/prosilveron6.th.jpg[/url does NOT work. When I click the Quote button the user didn't do [img]or%20anything.%20It%20was%20actually%20[url=website.com][img]image.xxx[/img]|http://www.blahblah.com]