Run this regression test on Ubuntu 16.04 with Unity.
It would fail, and the shaped foreground window would have some nebulous extension filling some 1/2 of the display area. It is apparently not a window itself since using xwininfo on that ghost reports the "Desktop" with full screen size -- actually, full virtual screen size since I use dual-screen system(s).
Tried on two (dual-screen) 16.04 with ATI and NVidia cards.
On 14.04 with Xfce4 and on Windows there's nothing like this.

The effect is manifested at least on jdk9 b111 (maybe earlier) and later, I tried some 122, 128, 132 and the current PIT build for b135.

RULE "java/awt/Window/ShapedAndTranslucentWindows/StaticallyShaped.java" Exception java.lang.RuntimeException: Background point ...