diff -r 1aa7eba26af5 -r bb871cb8ac06 lemon/core.h
--- a/lemon/core.h	Mon Apr 12 13:59:41 2010 +0200
+++ b/lemon/core.h	Tue Jun 22 15:39:26 2010 +0200
@@ -384,6 +384,7 @@
       template <typename From, typename NodeRefMap, typename ArcRefMap>
       static void copy(const From& from, Digraph &to,
                        NodeRefMap& nodeRefMap, ArcRefMap& arcRefMap) {
+        to.clear();
         for (typename From::NodeIt it(from); it != INVALID; ++it) {
           nodeRefMap[it] = to.addNode();
         }
@@ -411,6 +412,7 @@
       template <typename From, typename NodeRefMap, typename EdgeRefMap>
       static void copy(const From& from, Graph &to,
                        NodeRefMap& nodeRefMap, EdgeRefMap& edgeRefMap) {
+        to.clear();
         for (typename From::NodeIt it(from); it != INVALID; ++it) {
           nodeRefMap[it] = to.addNode();
         }