Some of the activities inside the ACP (such as removing members from a group) will forward me to a "Do you want to do this" confirmation page. When I click on the "YES" option, the page is linked back one directory too far. I can see that the "YES" button is using relative linking, and that it is linking to "./../../" which sends the form data to my website's hompage as opposed to the proper phpbb3.0 page.

Most other links on the ACP are hardcoded using the information I've provided in my setup config (http://url/forumdirectory).

Searching the support forums, I can see that mine is not an isolated case:

http://www.phpbb.com/community/viewtopic.php?f=46&t=728135

http://www.phpbb.com/community/viewtopic.php?f=46&t=727945

http://www.phpbb.com/community/viewtopic.php?f=46&t=711315

http://www.phpbb.com/community/viewtopic.php?f=46&t=688235

http://www.phpbb.com/community/viewtopic.php?f=46&t=585223