Adding background image disables drag drop of shape

Below is your sample code which works fine until I add a background image. I need to be able to drag and drop the rounded rectangle shapes even with a background image. Is there a way to do this?

 if (window.goSamples) goSamples();  // init for these samples -- you don't need to call this
      var $ = go.GraphObject.make;  // for conciseness in defining templates

      myDiagram =
        $(go.Diagram, "myDiagramDiv",
            initialContentAlignment: go.Spot.TopLeft,
            isReadOnly: true,  // allow selection but not moving or copying or deleting
            "toolManager.hoverDelay": 100  // how quickly tooltips are shown

      var $ = go.GraphObject.make;

        // the node template describes how each Node should be constructed
      myDiagram.nodeTemplate =
        $(go.Node, "Auto",  // the Shape automatically fits around the TextBlock
          $(go.Shape, "RoundedRectangle",  // use this kind of figure for the Shape
            // bind Shape.fill to
            new go.Binding("fill", "color")),
            { margin: 3 },  // some room around the text
            // bind TextBlock.text to
            new go.Binding("text", "key"))

        // the Model holds only the essential information describing the diagram
      myDiagram.model = new go.GraphLinksModel(
      [ // a JavaScript Array of JavaScript objects, one per node;
        // the "color" property is added specifically for this app
        { key: "Alpha", color: "lightblue" },
        { key: "Beta", color: "orange" },
        { key: "Gamma", color: "lightgreen" },
        { key: "Delta", color: "pink" }
      [ // a JavaScript Array of JavaScript objects, one per link
        { from: "Alpha", to: "Beta" },
        { from: "Alpha", to: "Gamma" },
        { from: "Beta", to: "Beta" },
        { from: "Gamma", to: "Delta" },
        { from: "Delta", to: "Alpha" }

      myDiagram.initialContentAlignment = go.Spot.Center;
        // enable Ctrl-Z to undo and Ctrl-Y to redo
      myDiagram.undoManager.isEnabled = true;

        // the background image, a floor plan
        $(go.Part,  // this Part is not bound to any model data
              layerName: "Background", position: new go.Point(0, 0),
              selectable: false, pickable: false
                    $(go.Picture, "/samples/myimg.png")

Did you mean to set Diagram.isReadOnly to true?

No. That worked, thank you!