So yesterday I was trading things all over the place, and there was a particular spike of lag at one point. When things went back to normal, the trade and arsenal windows registered twice (as if I had clicked them twice), and upon exiting them, they were stuck on my screen. Even after going to a new area, starting a Clockworks level, and logging in and out, they were still there, and even appeared on the login screen!
Eventually I exited out of the game itself and restarted it, which caused the windows to go away, but this has happened twice already, so I think it needs a fix!