Reproduce
Run toys HelloModality on Mac
1. Select WINDOW_MODAL
2. Create Dialog

Produces below stack trace:

     [java] ERROR: PrismPen / FX threads co-running: DIRTY: true UPLOAD: false WAITING: 0
     [java] FX: java.lang.Thread.dumpThreads(Native Method)
     [java] FX: java.lang.Thread.getAllStackTraces(Thread.java:1554)
     [java] FX: com.sun.javafx.tk.quantum.QuantumRenderer.checkRendererIdle(QuantumRenderer.java:286)
     [java] FX: com.sun.javafx.tk.quantum.QuantumToolkit.checkFxUserThread(QuantumToolkit.java:369)
     [java] FX: javafx.scene.Scene$ScenePulseListener.synchronizeSceneNodes(Scene.java:1726)
     [java] FX: javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:1858)
     [java] FX: com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:290)
     [java] FX: com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:393)
     [java] FX: com.sun.javafx.tk.quantum.QuantumToolkit$8.run(QuantumToolkit.java:319)
     [java] QR: com.sun.glass.ui.mac.MacView._end(Native Method)
     [java] QR: com.sun.glass.ui.View.unlock(View.java:507)
     [java] QR: com.sun.glass.ui.Pen.end(Pen.java:36)
     [java] QR: com.sun.javafx.tk.quantum.PresentingPainter.run(PresentingPainter.java:86)
     [java] QR: java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
     [java] QR: java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:317)
     [java] QR: java.util.concurrent.FutureTask.runAndReset(FutureTask.java:150)
     [java] QR: com.sun.prism.render.RenderJob.run(RenderJob.java:39)
     [java] QR: java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
     [java] QR: java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
     [java] QR: com.sun.javafx.tk.quantum.QuantumRenderer$PipelineRunnable.run(QuantumRenderer.java:102)
     [java] QR: java.lang.Thread.run(Thread.java:680)
     [java] ERROR: PrismPen / FX threads co-running: DIRTY: true UPLOAD: false WAITING: 0
     [java] FX: java.lang.Thread.dumpThreads(Native Method)
     [java] FX: java.lang.Thread.getAllStackTraces(Thread.java:1554)
     [java] FX: com.sun.javafx.tk.quantum.QuantumRenderer.checkRendererIdle(QuantumRenderer.java:286)
     [java] FX: com.sun.javafx.tk.quantum.QuantumToolkit.checkFxUserThread(QuantumToolkit.java:369)
     [java] FX: javafx.scene.Scene$MouseHandler.process(Scene.java:2781)
     [java] FX: javafx.scene.Scene$MouseHandler.pulse(Scene.java:2682)
     [java] FX: javafx.scene.Scene$MouseHandler.access$3300(Scene.java:2653)
     [java] FX: javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:1859)
     [java] FX: com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:290)
     [java] FX: com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:393)
     [java] FX: com.sun.javafx.tk.quantum.QuantumToolkit$8.run(QuantumToolkit.java:319)
     [java] QR: com.sun.glass.ui.mac.MacView._end(Native Method)
     [java] QR: com.sun.glass.ui.View.unlock(View.java:507)
     [java] QR: com.sun.glass.ui.Pen.end(Pen.java:36)
     [java] QR: com.sun.javafx.tk.quantum.PresentingPainter.run(PresentingPainter.java:86)
     [java] QR: java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
     [java] QR: java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:317)
     [java] QR: java.util.concurrent.FutureTask.runAndReset(FutureTask.java:150)
     [java] QR: com.sun.prism.render.RenderJob.run(RenderJob.java:39)
     [java] QR: java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
     [java] QR: java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
     [java] QR: com.sun.javafx.tk.quantum.QuantumRenderer$PipelineRunnable.run(QuantumRenderer.java:102)
     [java] QR: java.lang.Thread.run(Thread.java:680)
     [java] ERROR: PrismPen / FX threads co-running: DIRTY: true UPLOAD: false WAITING: 0
     [java] FX: java.lang.Thread.dumpThreads(Native Method)
     [java] FX: java.lang.Thread.getAllStackTraces(Thread.java:1554)
     [java] FX: com.sun.javafx.tk.quantum.QuantumRenderer.checkRendererIdle(QuantumRenderer.java:286)
     [java] FX: com.sun.javafx.tk.quantum.QuantumToolkit.checkFxUserThread(QuantumToolkit.java:369)
     [java] FX: javafx.scene.Scene$ScenePulseListener.synchronizeSceneNodes(Scene.java:1726)
     [java] FX: javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:1858)
     [java] FX: com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:290)
     [java] FX: com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:393)
     [java] FX: com.sun.javafx.tk.quantum.QuantumToolkit$8.run(QuantumToolkit.java:319)
     [java] QR: com.sun.glass.ui.mac.MacView._end(Native Method)
     [java] QR: com.sun.glass.ui.View.unlock(View.java:507)
     [java] QR: com.sun.glass.ui.Pen.end(Pen.java:36)
     [java] QR: com.sun.javafx.tk.quantum.PresentingPainter.run(PresentingPainter.java:86)
     [java] QR: java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
     [java] QR: java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:317)
     [java] QR: java.util.concurrent.FutureTask.runAndReset(FutureTask.java:150)
     [java] QR: com.sun.prism.render.RenderJob.run(RenderJob.java:39)
     [java] QR: java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
     [java] QR: java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
     [java] QR: com.sun.javafx.tk.quantum.QuantumRenderer$PipelineRunnable.run(QuantumRenderer.java:102)
     [java] QR: java.lang.Thread.run(Thread.java:680)
     [java] JavaFX application launcher: calling System.exit