Logged on tonight and this happened. Logged off, and my screen was fine in select world screen, etc. Logged in different ch 3 times. Still happened Restarted client once, still happened. Restarted client 2nd time, still happened. Restarted client 3rd time, stopped happening. Happens on more than 1 channel, and more than 1 map. Files are up to date, no files corrupted, running clean files.
This issue will definitely continue to happen until the client is fully closed. I used to experience this occasionally myself but haven't seen it in quite a long time now. Don't think there is a known fix for this but I'd suggest at least rebooting and see if that reduces the frequency of its occurrence.
