Situation:
* We have a JavaFx-app containing a SwingNode that has a JTextField and a JButton.
* The app was started with '-Djavafx.embed.singleThread=true'
* The text field has a focus-lost-listener that opens a JOptionPane
* The button has an action listener that opens a JOptionPane
* The text field is focussed


When the button is clicked, the following ClassCastException occurs:
{code}
Exception in thread "JavaFX Application Thread" java.lang.ClassCastException: java.lang.Thread cannot be cast to java.awt.EventDispatchThread
at java.awt.SequencedEvent.dispatch(SequencedEvent.java:106)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:749)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3$1.run(EventQueue.java:707)
at com.sun.javafx.application.PlatformImpl.lambda$null$170(PlatformImpl.java:295)
at com.sun.javafx.application.PlatformImpl$$Lambda$57/197317074.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(PlatformImpl.java:294)
at com.sun.javafx.application.PlatformImpl$$Lambda$56/1583804921.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._enterNestedEventLoopImpl(Native Method)
at com.sun.glass.ui.win.WinApplication._enterNestedEventLoop(WinApplication.java:128)
at com.sun.glass.ui.Application.enterNestedEventLoop(Application.java:511)
at com.sun.glass.ui.EventLoop.enter(EventLoop.java:107)
at com.sun.javafx.tk.quantum.QuantumToolkit.enterNestedEventLoop(QuantumToolkit.java:593)
at javafx.embed.swing.SwingFXUtils$FwSecondaryLoop.lambda$enter$63(SwingFXUtils.java:332)
at javafx.embed.swing.SwingFXUtils$FwSecondaryLoop$$Lambda$152/1201163521.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.runAndWait(PlatformImpl.java:317)
at com.sun.javafx.application.PlatformImpl.runAndWait(PlatformImpl.java:307)
at javafx.embed.swing.SwingFXUtils$FwSecondaryLoop.enter(SwingFXUtils.java:331)
at java.awt.Dialog.show(Dialog.java:1084)
at javax.swing.JOptionPane.showOptionDialog(JOptionPane.java:869)
at javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:666)
at javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:637)
at javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:608)
at JavaFxEDTClassCastException$2.actionPerformed(JavaFxEDTClassCastException.java:67)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.focusLost(BasicButtonListener.java:198)
at java.awt.Component.processFocusEvent(Component.java:6417)
at java.awt.Component.processEvent(Component.java:6281)
at java.awt.Container.processEvent(Container.java:2234)
at java.awt.Component.dispatchEventImpl(Component.java:4881)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1954)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:995)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:661)
at java.awt.Component.dispatchEventImpl(Component.java:4752)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:751)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:702)
at java.awt.EventQueue$3.run(EventQueue.java:696)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:724)
at java.awt.EventQueue$4.run(EventQueue.java:722)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:721)
at java.awt.SentEvent.dispatch(SentEvent.java:70)
at java.awt.DefaultKeyboardFocusManager$DefaultKeyboardFocusManagerSentEvent.dispatch(DefaultKeyboardFocusManager.java:217)
at java.awt.DefaultKeyboardFocusManager.sendMessage(DefaultKeyboardFocusManager.java:244)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:731)
at java.awt.Component.dispatchEventImpl(Component.java:4752)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:751)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:702)
at java.awt.EventQueue$3.run(EventQueue.java:696)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:724)
at java.awt.EventQueue$4.run(EventQueue.java:722)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:721)
at java.awt.SentEvent.dispatch(SentEvent.java:70)
at java.awt.DefaultKeyboardFocusManager$DefaultKeyboardFocusManagerSentEvent.dispatch(DefaultKeyboardFocusManager.java:217)
at java.awt.DefaultKeyboardFocusManager.sendMessage(DefaultKeyboardFocusManager.java:244)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:348)
at java.awt.Component.dispatchEventImpl(Component.java:4752)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:751)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:702)
at java.awt.EventQueue$3.run(EventQueue.java:696)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:724)
at java.awt.EventQueue$4.run(EventQueue.java:722)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:721)
at java.awt.SequencedEvent.dispatch(SequencedEvent.java:128)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:749)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3$1.run(EventQueue.java:707)
at com.sun.javafx.application.PlatformImpl.lambda$null$170(PlatformImpl.java:295)
at com.sun.javafx.application.PlatformImpl$$Lambda$57/197317074.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(PlatformImpl.java:294)
at com.sun.javafx.application.PlatformImpl$$Lambda$56/1583804921.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._enterNestedEventLoopImpl(Native Method)
at com.sun.glass.ui.win.WinApplication._enterNestedEventLoop(WinApplication.java:128)
at com.sun.glass.ui.Application.enterNestedEventLoop(Application.java:511)
at com.sun.glass.ui.EventLoop.enter(EventLoop.java:107)
at com.sun.javafx.tk.quantum.QuantumToolkit.enterNestedEventLoop(QuantumToolkit.java:593)
at javafx.embed.swing.SwingFXUtils$FwSecondaryLoop.lambda$enter$63(SwingFXUtils.java:332)
at javafx.embed.swing.SwingFXUtils$FwSecondaryLoop$$Lambda$152/1201163521.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.runAndWait(PlatformImpl.java:317)
at com.sun.javafx.application.PlatformImpl.runAndWait(PlatformImpl.java:307)
at javafx.embed.swing.SwingFXUtils$FwSecondaryLoop.enter(SwingFXUtils.java:331)
at java.awt.Dialog.show(Dialog.java:1084)
at javax.swing.JOptionPane.showOptionDialog(JOptionPane.java:869)
at javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:666)
at javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:637)
at javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:608)
at JavaFxEDTClassCastException$1.focusLost(JavaFxEDTClassCastException.java:56)
at java.awt.AWTEventMulticaster.focusLost(AWTEventMulticaster.java:230)
at java.awt.Component.processFocusEvent(Component.java:6417)
at java.awt.Component.processEvent(Component.java:6281)
at java.awt.Container.processEvent(Container.java:2234)
at java.awt.Component.dispatchEventImpl(Component.java:4881)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1954)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:995)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:661)
at java.awt.Component.dispatchEventImpl(Component.java:4752)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:751)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3$1.run(EventQueue.java:707)
at com.sun.javafx.application.PlatformImpl.lambda$null$170(PlatformImpl.java:295)
at com.sun.javafx.application.PlatformImpl$$Lambda$57/197317074.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(PlatformImpl.java:294)
at com.sun.javafx.application.PlatformImpl$$Lambda$56/1583804921.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$145(WinApplication.java:101)
at com.sun.glass.ui.win.WinApplication$$Lambda$38/1463642169.run(Unknown Source)
at java.lang.Thread.run(Thread.java:745)
{code}

When the app is started without '-Djavafx.embed.singleThread=true', no exception is thrown (and the two message boxes are shown)