confirm_box() adds duplicate strings to URLs in extensions

Updated a site to phpBB 3.2.2-RC1. After the update, the confirm_box() function in my extension no longer works. Clicking on "Yes" or "No" produces the same result - extra text added to the URL. The 1st code is with URL rewriting enabled, the second is with URL rewriting disabled.

http://www.project-w.local/community/answer/answer/mark_answer?p=2&confirm_key=82ZFNE6AF8

http://www.project-w.local/community/app.php/answer/app.php/answer/mark_answer?p=2&confirm_key=82ZFNE6AF8

You'll notice that it's adding additional "answer" and "app.php/answer" respectively. Extension worked fine in phpBB 3.2.1.

Relevant code: controller