If an administrator goes out to test another user's permissions and then tries to look at the UCP to see what that user's permission mask gives access to there, they will find that the UCP will just be stuck on Front Page in the Overview tab, with none of the tabs or buttons working. 

I do not know if this bug was introduced in phpBB 3.3.13 or 3.3.12, but either way, this issue was not present in phpBB 3.3.11 or below.

I have observed this issue with 3.3.13 on my site, a test localhost board, and even at http://www.try-phpbb.com/33x, so this does not seem to just be an issue with my install. I have also observed this issue both in Firefox and Edge, so it is not a cache issue either.

Attached is an image of the bug. In the url bar, it shows that it is supposed to be on the Attachment's section when it is stuck on the Front Page. Trying to navigate to different tabs up top has the same effect too. It gets stuck on that page.