I've tried everything I could think of but I've not been able to solve this annoying problem:

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.

Looks like we're running the same OS, but I don't have those problems. I suppose you're sure it isn't using openjdk? Sometimes, when a window pops up (e.g., resign, game over) it is blank, but minimizing then maximizing the window solves it.

It can't be openjdk as I installed it on purpose to test this.
Also, the splash screen clearly states it's the Oracle JRE. (Oracle bought Sun)

Try turning off the window effects in Linux. I've seen similar problems before when they were on. Seems it wakes up bugs in the java GUI.

I've just turned them off, let's see what happens.
I've already seen a few artifacts (over the "Black to play" and move count), but nothing compared to what it was before. I don't seem to be able to reproduce the bug again, but this isn't exactly an exact science..
I'll keep things this way for a while. If I don't report back it means things are running smoothly.
I'm sure I'll remember this thread if they come back, so let's hope I don't.

Finnaly got some time to play but the news are not good: the problem did not vanish.

Sorry, that's the only advice I can give - when I turn off the window effects the problem disappears for me.

Only thought I have is to make sure your libraries and your video drivers are up to date.

Also, have you tried reinstalling the application?

--
Bill