fix a really nasty bug in OrderedContainer that occurs with duplication errors (now key errors).

CHANGES.txt

@@ -4,6 +4,9 @@ CHANGES
 
 3.8.2 (unreleased)
 ------------------
+- Fix a bug in OrderedContainer where trying to set the value for a
+  key that already exists (duplication error) would actually delete the
+  key from the order, leaving a dangling reference.
 
 - Partially break dependency on ``zope.traversing`` by disusing
   zope.traversing.api.getPath in favor of using

src/zope/container/ordered.py

@@ -179,6 +179,13 @@ class OrderedContainer(Persistent, Contained):
         ['foo', 'baz']
         >>> int(len(oc._order) == len(oc._data))
         1
+
+        >>> oc['foo'] = 'baz'
+        Traceback (most recent call last):
+        ...
+        KeyError: u'foo'
+        >>> oc._order
+        ['foo', 'baz']
         """
 
         existed = self._data.has_key(key)
@@ -207,7 +214,8 @@ class OrderedContainer(Persistent, Contained):
         try:
             setitem(self, self._data.__setitem__, key, object)
         except Exception, e:
-            self._order.remove(key)
+            if not existed:
+                self._order.remove(key)
             raise e
 
         return key