At first there's SceneBuilder 2 that is hit by the use of SwingNode: as soon as you drop a SwingNode taken from the Library onto the Content it becomes impossible to exit from SceneBuilder, the window goes away but the process remains. It is logged as DTL-5861.

I created a very small FX app where in the FXML we read this:

<AnchorPane id="AnchorPane" prefHeight="200" prefWidth="320" xmlns:fx="http://javafx.com/fxml" fx:controller="javafxapplicationswingnode.FXMLDocumentController">
    <children>
        <Button layoutX="126" layoutY="90" text="Click Me!" onAction="#handleButtonAction" fx:id="button" />
        <Label layoutX="126" layoutY="120" minHeight="16" minWidth="69" fx:id="label" />
        <SwingNode>
          <content>
            <JButton text="This is a JButton" />
          </content>
        </SwingNode>
    </children>
</AnchorPane>

When trying to run such an app (Mac + FX 8 b115) nothing will ever come up. Apparently the FXMLLoader does its part of the job but no rendering is done.

Then I've put as VM option -Djavafx.pulseLogger=true and this is enough to get the application running correctly, and with the process properly dying at exit time.
I suspect the activation of the debug traces slows the picture enough so that the rendering becomes correct.
I cannot be sure the issue seen with the small app is the same than the one that hist SceneBuilder 2: both use the a SwingNode containing a JButton.

The impact on SceneBuilder 2 occurs on all platform (MAc, Win, Linux); I ran the small app only on Mac.