--- a/mercurial/dirstate.py	Sun Jun 15 13:01:01 2008 +0200
+++ b/mercurial/dirstate.py	Sun Jun 15 13:01:03 2008 +0200
@@ -167,6 +167,8 @@
         self._dirty = False
 
     def copy(self, source, dest):
+        if source == dest:
+            return
         self._dirty = True
         self._copymap[dest] = source