XF 1.4 Closing pop-up window leads to undefined


Well-known member
I noticed that if you close a pop-up window such as those that open when you click a username, the page redirects to URL.com/undefined.

I.e Click username>Mini Profile Popup>Click "X" in top right>Redirect to /undefined.

What is causing this? I never recall this happening until recently, but I have not made any recent changes.