Java version: Mustang b49 and later, not reproducible on b42-b48
Platform: reproducible on SuSE 9.2 & 9.3, XToolkit
Reproducibility: quite often (3/4).

When running attached test on XToolkit, mustang b49 and later following exception is generated
java.lang.NullPointerException
        at sun.awt.image.VolatileSurfaceManager.displayChanged(VolatileSurfaceManager.java:310)
        at sun.awt.SunDisplayChanger.notifyListeners(SunDisplayChanger.java:102)
        at sun.awt.X11GraphicsEnvironment.displayChanged(X11GraphicsEnvironment.java:1062)
        at sun.awt.X11GraphicsDevice.setDisplayMode(X11GraphicsDevice.java:365)
        at sun.awt.X11GraphicsDevice.setFullScreenWindow(X11GraphicsDevice.java:269)
        at FrameFullScreenTest.fullScreenSameDevice(FrameFullScreenTest.java:129)
        at FrameFullScreenTest.<init>(FrameFullScreenTest.java:22)
        at FrameFullScreenTest.main(FrameFullScreenTest.java:157)

See 6290240 for details on test.

This bug is reproducible starting from b49 but similar exceptions can be thrown on earlier builds.