Edge and vertex overlapping in mxStack Layout

ClassDiagram.scala

import java.awt.{ Dimension}
import scala.swing.{ BoxPanel, Component}
import scala.swing.{ Orientation}
import com.mxgraph.layout.mxStackLayout
import com.mxgraph.model.mxCell
import com.mxgraph.swing.mxGraphComponent
import com.mxgraph.view.mxGraph
import com.mxgraph.util.mxConstants
import com.mxgraph.view.mxEdgeStyle
import com.mxgraph.layout.hierarchical.mxHierarchicalLayout
import com.mxgraph.layout.mxOrganicLayout
import com.mxgraph.layout.mxCompactTreeLayout

class ClassDiagramPanel extends BoxPanel(Orientation.Vertical) {
  preferredSize = new Dimension(800, 600)

  private def createGraph(graphPopulater: mxGraph => Unit) = {
    contents.clear
    val graph = new mxGraph
    val style = graph.getStylesheet.getDefaultEdgeStyle //.put(mxConstants., mxEdgeStyle.EntityRelation)
    graph.getModel.beginUpdate()
    graphPopulater(graph)
    graph.getModel.endUpdate()

    val layout = new mxStackLayout(graph, true, 30)
    layout.execute(graph.getDefaultParent)

    val graphComponent = new mxGraphComponent(graph)
    graphComponent.setEnabled(false)
    contents += Component.wrap(graphComponent)
    revalidate

  }

  private def makeClassNode(collectionName: String, graph: mxGraph) = {

    val defParent = graph.getDefaultParent

    val parent = graph.insertVertex(defParent, null, collectionName, 20, 20, 80, 24, "fillColor=#AAAAFF;fontSize=22;fontStyle=1;fontFamily=Ubuntu, Arial, Helvetica, sans-serif;fontColor=#000000")
    var vertices = List[AnyRef]()
    (1 to 9).map("e " + ) foreach { value =>
      val vertex = graph.insertVertex(parent, null, value, 0, 0, 80, 24, "fillColor=#AAAAAA;fontSize=18;fontFamily=Ubuntu, Arial, Helvetica, sans-serif;portConstraint=eastwest;fontColor=#000000")
      vertices :+= vertex
    }

    val allCells = parent :: vertices
    val layout = new mxStackLayout(graph, false)
    allCells.foreach(graph.updateCellSize)
    allCells.foreach(layout.execute)

    vertices
  }

  private val randomGenerator = new java.util.Random(1)
  private def getRandomInt(max:Int) = randomGenerator.nextInt(max)

  private def pickRandom[T](l:Seq[T]) = l(getRandomInt(l.length))

  private def pickRandom[T](l:Seq[T], avoid: T) = {
    var chosen:T = avoid
    while (avoid equals chosen) {
      chosen = l(getRandomInt(l.length))
    }
    chosen
  }

  private def getAnEdge(verticeList:List[List[Any]]) = {
    val firstParent = pickRandom(verticeList)
    val firstCell = pickRandom(firstParent)

    val secondParent = pickRandom(verticeList, firstParent)
    val secondCell = pickRandom(secondParent)

    (firstCell -> secondCell)
  }

  def drawRelation = {
    createGraph { graph =>

      var vertexRelations = List[List[Any]]()

      (1 to 8).map("obj "+) foreach { name =>
        val vertexRelation = makeClassNode(name, graph)
        vertexRelations :+= vertexRelation

      }

      val defParent = graph.getDefaultParent
      (0 until 4) foreach {i =>

        val edge = getAnEdge(vertexRelations)
        graph.insertEdge(defParent, null, " ", edge._1, edge._2, "edgeStyle=orthogonalEdgeStyle;strokeWidth=5;strokeColor=#8AA63D;")

      }
    }
  }
}