Model#addNodeData not apply with TreeLayout.comparer

GoJS
1 
....
layout: graph(TreeLayout, {
        sorting: TreeLayout.SortingAscending,
        arrangement: TreeLayout.ArrangementFixedRoots,
        comparer: function (a, b) {
          var ay = a.node ? a.node.location.y : 0
          var by = b.node ? b.node.location.y : 0
          if (isNaN(ay) || isNaN(by)) return 0
          if (ay < by) return -1
          if (ay > by) return 1
          return 0
        }
      }),
...

myDiagram.model.addNodeData({parent: 1, loc: '0 100', content: 'test'})
2

I just tried this, and it worked as I think you are expecting.

      $(go.Diagram, . . .,
        {
          layout: $(go.TreeLayout, {
            sorting: go.TreeLayout.SortingAscending,
            comparer: function(va, vb) {
              var da = va.node.data;
              var db = vb.node.data;
              if (da.text < db.text) return -1;
              if (da.text > db.text) return 1;
              return 0;
            }
          }),

    myDiagram.model = new go.GraphLinksModel(
    [
      { key: 3, text: "Gamma", color: "lightgreen" },
      { key: 4, text: "Delta", color: "pink" },
      { key: 1, text: "Alpha", color: "lightblue" },
      { key: 2, text: "Beta", color: "orange" }
    ],
    [
      { from: 1, to: 2 },
      { from: 3, to: 4 }
    ]);

    myDiagram.model.commit(function(m) {
      m.addNodeData({ text: "Ccc" });
    }, "added root node");