Start SceneBuilder.
Take menubar > File > Open
Exit from the tool (via menubar): the main SceneBuilder window goes away but the process remains live.
The SceneBuilder process is hanged. If you kill the file chooser window it triggers the stack below but still the process doesn't die.

On Win and Linux there's no such issue because the lack of system menu bar prevents from taking menu Exit action while file chooser is opened. You can only dismiss the main SceneBuilder window by clicking on the decoration exit button but nothing harms, and eventually you close the file chooser then the process terminates.

Exception in thread "JavaFX Application Thread" java.lang.IllegalStateException: This operation is permitted on the event thread only; currentThread = JavaFX Application Thread
at com.sun.glass.ui.Application.checkEventThread(Application.java:427)
at com.sun.glass.ui.EventLoop.leave(EventLoop.java:159)
at com.sun.glass.ui.mac.MacApplication._enterNestedEventLoopImpl(Native Method)
at com.sun.glass.ui.mac.MacApplication._enterNestedEventLoop(MacApplication.java:113)
at com.sun.glass.ui.Application.enterNestedEventLoop(Application.java:495)
at com.sun.glass.ui.EventLoop.enter(EventLoop.java:107)
at com.sun.glass.ui.mac.MacCommonDialogs._showFileOpenChooser(Native Method)
at com.sun.glass.ui.mac.MacCommonDialogs.showFileChooser_impl(MacCommonDialogs.java:59)
at com.sun.glass.ui.mac.MacApplication.staticCommonDialogs_showFileChooser(MacApplication.java:264)
at com.sun.glass.ui.CommonDialogs.showFileChooser(CommonDialogs.java:212)
at com.sun.javafx.tk.quantum.QuantumToolkit.showFileChooser(QuantumToolkit.java:1424)
at javafx.stage.FileChooser.showDialog(FileChooser.java:416)
at javafx.stage.FileChooser.showOpenMultipleDialog(FileChooser.java:373)
at com.oracle.javafx.scenebuilder.app.SceneBuilderApp.performOpenFile(SceneBuilderApp.java:394)
at com.oracle.javafx.scenebuilder.app.SceneBuilderApp.performControlAction(SceneBuilderApp.java:136)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$ApplicationControlActionController.perform(MenuBarController.java:1545)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController.handleOnActionMenu(MenuBarController.java:1080)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController.access$800(MenuBarController.java:88)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$20.handle(MenuBarController.java:1073)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$20.handle(MenuBarController.java:1069)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:204)
at javafx.scene.control.MenuItem.fire(MenuItem.java:462)
at com.sun.javafx.scene.control.GlobalMenuAdapter$5.handle(GlobalMenuAdapter.java:158)
at com.sun.javafx.scene.control.GlobalMenuAdapter$5.handle(GlobalMenuAdapter.java:156)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:204)
at javafx.scene.control.MenuItem.fire(MenuItem.java:462)
at com.sun.javafx.tk.quantum.GlassSystemMenu$6.action(GlassSystemMenu.java:234)