new file mode 100644

@@ -0,0 +1,10 @@

+digraph {

+  {

+    node [ shape=box ]

+    a

+    b

+  }

+  {

+    a -> b

+  }

+}

@@ -488,11 +488,12 @@ class XDotParser(DotParser):

             pos = attrs['pos']

         except KeyError:

             # Node without pos attribute, most likely a subgraph.  We need to

-            # create a Node object nevertheless, so that any edges to/from it

-            # don't get lost.

-            # TODO: Extract the position from subgraph > graph > bb attribute.

-            node = elements.Node(id, 0.0, 0.0, 0.0, 0.0, [], None, None)

-            self.node_by_name[id] = node

+            # create a Node object nevertheless, when one doesn't exist

+            # already, so that any edges to/from it don't get lost.

+            if id not in self.node_by_name:

+                # TODO: Extract the position from subgraph > graph > bb attribute.

+                node = elements.Node(id, 0.0, 0.0, 0.0, 0.0, [], None, None)

+                self.node_by_name[id] = node

             return

         x, y = self.parse_node_pos(pos)