Since the most recent patch it appears that when pressing 'Esc' to bring up the logoff window / Video / Audio settings, etc.. it can occasionally get stuck on screen. Clicking on the 'Log Off' 'Accept' 'Cancel' 'Quit' buttons has no effect and if you press 'Esc' again the same menu shows (when it should disappear) and buttons still fail to work.

The only remedy is to C-A-D (Ctrl, Alt, Delete) into task manager and end the Java process. A right royal pain if you've only opened to it to switch to a window whilst you wait (up to half an hour) for a gate that you wish to play (i.e Arena farming after the Terminal).