Wrong (?) order of calls to TraversalListener methods in DepthFirstIterator

[PeteS4]

 * JGraphT version: 1.5.1
 * Java version (java -version)/platform:  Kotlin, jvmTarget 1.8

Issue

The order in which the traversed methods of a TraversalListener for a DepthFirstIterator are called seems wrong to me. I would expect that edges would always be traversed right before the vertex they are leading to. Instead, for a branching point, all outgoing edges are traversed, and then the traversal is continued from one of the edge's targets.

Steps to reproduce (small coding example)

val graph = SimpleDirectedGraph<String, DefaultEdge>(DefaultEdge::class.java)
graph.addVertex("1")
graph.addVertex("2")
graph.addVertex("3")
graph.addVertex("4")
graph.addEdge("1", "2")
graph.addEdge("1", "3")
graph.addEdge("2", "4")
graph.addEdge("3", "4")
class MyListener(): TraversalListener<String, DefaultEdge> {
  override fun connectedComponentFinished(e: ConnectedComponentTraversalEvent) {}
  override fun connectedComponentStarted(e: ConnectedComponentTraversalEvent) {}
  override fun edgeTraversed(e: EdgeTraversalEvent<DefaultEdge>) {
    println("visit edge ${e.edge}")
  }
  override fun vertexTraversed(e: VertexTraversalEvent<String>) {
    println("visit vertex ${e.vertex}")
  }
  override fun vertexFinished(e: VertexTraversalEvent<String>) {}
}
val listener = MyListener()
val iterator = DepthFirstIterator(graph, "1")
iterator.addTraversalListener(listener)
iterator.forEach { _ -> }

Expected behaviour

I would expect to get as output:

visit vertex 1
visit edge (1 : 2)
visit vertex 2
visit edge (2 : 4)
visit vertex 4
visit edge (1 : 3)
visit vertex 3
visit edge (3 : 4)

Instead I get:

visit vertex 1
visit edge (1 : 2)
visit edge (1 : 3)
visit vertex 3
visit edge (3 : 4)
visit vertex 4
visit vertex 2
visit edge (2 : 4)