There are reports in the Java Bug database, that explian this problem. Most often this occurs with the support of DirectX, due to hardware video accelerators that don't implement correctly some off-screen redraw buffers. The problem is not directly within Java, but is due to the fact that some video drivers do not report correctly that they don't support some accelerated options.

If you experiment this problem, you may disable Direct3D in Java, or all DirectX. See the Java support forums for details of the setting...

In Windows, you may also try to upgrade DirectX and use the Microsoft certified drivers instead of the "accelerated" drivers that some manufacturer propose. Generally this solves the problem. If this does not work, reduce the acceleration options in the system control panel. This should disable the support of off-screen buffers by the hardware, and use a software emulation.

Some other options can cause problems in DirectX: for example, on Windows XP, the "ClearType" smoothed fonts renferer has some bugs, and it can draw on pixels that were not part of the buffer. This problem occurs with many old display drivers, which assume that a character cannot be drawn on a larger area than its "visible" width.

The impact is that, in some cases, the character may be drawn with some pixels out of the off-screen buffer. This problem is visible when you open a DOS window and display a string of "w" characters: you'll see that the right edge of the character is sometimes displayed correctly, sometimes it is truncated, depending on the operation you perform. This can also be visible when, sometimes, the text of a title bar is drawn on the wrong place on the screen, in case of heavy CPU load. The problem is due to both a bug in Windows XP, and in the display driver...

Try disabling the smoothed fonts renderer in the display setting...