FULL PRODUCT VERSION :
java version "1.8.0_92"
Java(TM) SE Runtime Environment (build 1.8.0_92-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.92-b14, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.1.7601]

A DESCRIPTION OF THE PROBLEM :
I embedded a JavaFX button in a SWT application using FXCanvas. When the JavaFX button is pressed a modal JavaFX dialog appears.
- if I click on any SWT UI the SWT window is shown on top of the dialog
- if I press a SWT button the events a cashed and performed as soon as I closed the dialog

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
- start the sample application
- press the JavaFX button to show the modal dialog
- click on the SWT button
- close the dialog

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
- the dialog should remain on top
- the click on the SWT button should be ignored
ACTUAL -
- the dialog is behind the SWT window
- the clicks are performed as soon as the dialog has been closed

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javafx.embed.swt.FXCanvas;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Alert;
import javafx.scene.control.Button;
import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.layout.RowLayout;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class JavaFxInSwtModalDialogBug {

  public static void main(String[] args) {
    Display display = new Display();
    Shell shell = new Shell(display);
    shell.setLayout(new RowLayout());
 
    org.eclipse.swt.widgets.Button swtButton = new org.eclipse.swt.widgets.Button(shell, SWT.PUSH);
    swtButton.setText("SWT Button");

    FXCanvas fxCanvas = new FXCanvas(shell, SWT.NONE) {
      @Override
      public Point computeSize(int wHint, int hHint, boolean changed) {
        getScene().getWindow().sizeToScene();
        int width = (int) getScene().getWidth();
        int height = (int) getScene().getHeight();
        return new Point(width, height);
      }
    };

    Button jfxButton = new Button("JFX Button");
    fxCanvas.setScene(new Scene(new Group(jfxButton)));
 
    swtButton.addListener(SWT.Selection, event -> System.out.println("SWT has been clicked!"));
    jfxButton.setOnAction(event -> new Alert(Alert.AlertType.INFORMATION).showAndWait());

    shell.open();
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        display.sleep();
      }
    }
    display.dispose();
  }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use a SWT dialog instead.