The QR box was made to always be displayed uncollapsed when enabled. People who are viewing a topic after clicking the First Unread Post link may be brought to a page that isn't the last page, but not realize that. So when they go to reply, they may reply to a post that has already been replied to because they haven't seen the next few pages.

To prevent this, it was decided (https://area51.phpbb.com/phpBB/viewtopic.php?f=108&t=42923) to put the code used to collapse the QR box (only found in Prosilver) that was removed, and have it collapsed by default except on the final page of the topic.