FULL PRODUCT VERSION :
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.1.7601]

EXTRA RELEVANT SYSTEM CONFIGURATION :
No special configuration requirements. Also confirmed on OS X 10.11.1

A DESCRIPTION OF THE PROBLEM :
Placing 2+ SwingNode objects in a JFXPanel contained in a JFrame causes the application to come to a crawl upon one of the JComponents within the SwingNodes receiving focus.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1) Create a JFrame window
2) Put a JFXPanel in the window
3) Create a GridPane
4) Create two SwingNode objects, each containing a JToggleButton
5) Place the SwingNode objects on the GridPane
6) Set the JFXPanel scene to a scene with the GridPane
7) Show the JFrame
8) Click one of the toggle buttons
9) Click the toggle button again

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Application toggles and untoggles the button
ACTUAL -
Application toggles the button after a short delay, and then freezes.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javax.swing.*;

import javafx.application.Platform;
import javafx.embed.swing.JFXPanel;
import javafx.embed.swing.SwingNode;
import javafx.scene.Scene;
import javafx.scene.control.ToggleButton;
import javafx.scene.layout.ColumnConstraints;
import javafx.scene.layout.GridPane;

public class SwingNodeTest {
    private static Scene createScene(JComponent button1, JComponent button2) {
        GridPane pane = new GridPane();
        pane.getColumnConstraints().add(new ColumnConstraints(100));
        pane.getColumnConstraints().add(new ColumnConstraints(200));

        SwingNode node1 = new SwingNode();
        // Best practice to call SwingNode->setContent(...) on the EDT, but doesn't make
        // a difference for the test.
        node1.setContent(button1);
        pane.add(node1, 0, 0);

        ToggleButton node2 = new ToggleButton("2");
        // Commenting out the above line and uncommenting the below lines cause EXTREME
        // Performance degradation.
// SwingNode node2 = new SwingNode();
// node2.setContent(button2);
        pane.add(node2, 1, 0);

        return new Scene(pane);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                JFXPanel panel = new JFXPanel();
                frame.setSize(800, 600);
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setContentPane(panel);
                frame.setVisible(true);

                JButton button1 = new JButton("1");
                JToggleButton button2 = new JToggleButton("2");

                Platform.runLater(new Runnable() {
                    @Override
                    public void run() {
                        final Scene scene = createScene(button1, button2);
                        panel.setScene(scene);
                    }
                });
            }
        });
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Restricting SwingNode usage within JFXPanels under JFrames is the only workaround known ATM. This restricts our ability to use JavaFX, as we are heavily invested in custom Swing components/containers.