Logged in with another user's nickname showing, security error popup

[WakeX]

I believe that's kinda bad :

Another user's name (who does exist and posted messages a few months ago too) showed up and the notification showed 2 alerts when I myself only got one after I refreshed the page.

I didn't screenshot the security error but it was a popup from the forum.

Edit - Just happened again with a different username, this time with error popup included:

 

[Alan J T]

Being looked in to now