I have attached a test program to reproduce this.

1) Open dist/FullScreenSetScene.html in a browser (I used IE9)
2) Click the Switch Scene button
3) Press <ESC> to exit full-screen mode

Step #2 causes an NPE so that when you exit from full screen mode the window will not be restored in the browser.

If you run the program in standalone mode (dist/FullScreenSetScene.jar) or WebStart mode (dist/FullScreenSetScene.jnlp) it runs fine (except that the size of the window is incorrect after switching scenes due to RT-20216).