Program: 51009
Project: 51009
Buggy source:
/** 
 * First step in the Weisfeiler-Lehman algorithm, applied to directedgraphs with edge labels.
 * @param graphs
 * @param startLabel
 * @param currentLabel
 */
private void relabelGraphs2MultisetLabels(List<DirectedMultigraphWithRoot<Vertex<StringBuffer>,Edge<StringBuffer>>> graphs,int startLabel,int currentLabel){
  Map<String,Bucket<Vertex<StringBuffer>>> bucketsV=new HashMap<String,Bucket<Vertex<StringBuffer>>>();
  Map<String,Bucket<Edge<StringBuffer>>> bucketsE=new HashMap<String,Bucket<Edge<StringBuffer>>>();
  for (int i=startLabel; i < currentLabel; i++) {
    bucketsV.put(Integer.toString(i),new Bucket<Vertex<StringBuffer>>(Integer.toString(i)));
    bucketsE.put(Integer.toString(i),new Bucket<Edge<StringBuffer>>(Integer.toString(i)));
  }
  for (  DirectedGraph<Vertex<StringBuffer>,Edge<StringBuffer>> graph : graphs) {
    for (    Edge<StringBuffer> edge : graph.getEdges()) {
      bucketsV.get(edge.getLabel()).getContents().add(graph.getDest(edge));
    }
    for (    Vertex<StringBuffer> vertex : graph.getVertices()) {
      Collection<Edge<StringBuffer>> v2=graph.getOutEdges(vertex);
      bucketsE.get(vertex.getLabel()).getContents().addAll(v2);
    }
  }
  for (  DirectedGraph<Vertex<StringBuffer>,Edge<StringBuffer>> graph : graphs) {
    for (    Edge<StringBuffer> edge : graph.getEdges()) {
      edge.setLabel(edge.getLabel().append("String_Node_Str"));
    }
    for (    Vertex<StringBuffer> vertex : graph.getVertices()) {
      vertex.setLabel(vertex.getLabel().append("String_Node_Str"));
    }
  }
  for (int i=startLabel; i < currentLabel; i++) {
    Bucket<Vertex<StringBuffer>> bucketV=bucketsV.get(Integer.toString(i));
    for (    Vertex<StringBuffer> vertex : bucketV.getContents()) {
      vertex.getLabel().append(bucketV.getLabel());
    }
    Bucket<Edge<StringBuffer>> bucketE=bucketsE.get(Integer.toString(i));
    for (    Edge<StringBuffer> edge : bucketE.getContents()) {
      edge.getLabel().append(bucketE.getLabel());
    }
  }
}

Fixed version (ground truth):
/** 
 * First step in the Weisfeiler-Lehman algorithm, applied to directedgraphs with edge labels.
 * @param graphs
 * @param startLabel
 * @param currentLabel
 */
private void relabelGraphs2MultisetLabels(List<DirectedMultigraphWithRoot<Vertex<StringBuffer>,Edge<StringBuffer>>> graphs,int startLabel,int currentLabel){
  Map<String,Bucket<Vertex<StringBuffer>>> bucketsV=new HashMap<String,Bucket<Vertex<StringBuffer>>>();
  Map<String,Bucket<Edge<StringBuffer>>> bucketsE=new HashMap<String,Bucket<Edge<StringBuffer>>>();
  for (int i=startLabel; i < currentLabel; i++) {
    bucketsV.put(Integer.toString(i),new Bucket<Vertex<StringBuffer>>(Integer.toString(i)));
    bucketsE.put(Integer.toString(i),new Bucket<Edge<StringBuffer>>(Integer.toString(i)));
  }
  for (  DirectedMultigraphWithRoot<Vertex<StringBuffer>,Edge<StringBuffer>> graph : graphs) {
    for (    Edge<StringBuffer> edge : graph.getEdges()) {
      bucketsV.get(edge.getLabel().toString()).getContents().add(graph.getDest(edge));
    }
    for (    Vertex<StringBuffer> vertex : graph.getVertices()) {
      Collection<Edge<StringBuffer>> v2=graph.getOutEdges(vertex);
      bucketsE.get(vertex.getLabel().toString()).getContents().addAll(v2);
    }
  }
  for (  DirectedMultigraphWithRoot<Vertex<StringBuffer>,Edge<StringBuffer>> graph : graphs) {
    for (    Edge<StringBuffer> edge : graph.getEdges()) {
      edge.setLabel(edge.getLabel().append("String_Node_Str"));
    }
    for (    Vertex<StringBuffer> vertex : graph.getVertices()) {
      vertex.setLabel(vertex.getLabel().append("String_Node_Str"));
    }
  }
  for (int i=startLabel; i < currentLabel; i++) {
    Bucket<Vertex<StringBuffer>> bucketV=bucketsV.get(Integer.toString(i));
    for (    Vertex<StringBuffer> vertex : bucketV.getContents()) {
      vertex.getLabel().append(bucketV.getLabel());
    }
    Bucket<Edge<StringBuffer>> bucketE=bucketsE.get(Integer.toString(i));
    for (    Edge<StringBuffer> edge : bucketE.getContents()) {
      edge.getLabel().append(bucketE.getLabel());
    }
  }
}