Every game window I open after the first one (whether the first game window is already closed or not) appears with artifacts all over it.
Here is an example:

I've tried both Sun Java 6 and OpenJDK.
Is there a known solution to this?
These artifacts disappear when I move the mouse over them (for example, the buttons will become visible when I move my mouse over them), so to me it seems that it has something to do with the correct refreshing of the window.
However, the spectator's list and the players nicknames are sometimes not updated, so it could also be a variable not reinitialized (tough it would be strange in Java..).. These are just my wild programmer guesses without looking at the source code, but I would be glad to help in anything needed.