When the splash screen is visible and when it has the focus, pressing ALT+Right click on the splash screen brings up the menu on gnome.

public class CloseSplashScreenTest {
    public static void main(String[] args) {
        try { Thread.sleep(10000); } catch (Exception e) {}
    }
}
Step to reproduce:
-------------------
1) Run the above program.
java -splash:garden.jpg <filename>
2) minimize all the windows on the screen.
3) click on the splash screen.
4) Press ALT + right click on the splash screen. If menu is appeared then bug is reproduced.
I tested this on mustang b104.