Confirmed this bug. Cannot exit out of the Mac System's Full Screen Mode. I don't mean the full screen mode in the drawing area, but the one activated by clicking the green dot in the app window. The upper right buttons (Cleanup, PltEdit, InknPaint, etc) are doubled in another row above one another. I'd take a screen shot, but I can't when the app in full screen in it's own space. there is no way in the app to exit the system's fullscreen mode.
Solution: I removed the application and deleted the preferences in ~/Library/Preferences (While in the finder; hold Opt and click "GO" in the top bar, select Library, then navigate to Preferences.) that got me back to the windowed view. Remember to hold Option when you click on the Green button to expand the window to the size of your screen without going in to Full Screen Mode.