weakref doc clarification

Doc/library/weakref.rst

--- a/Doc/library/weakref.rst	Wed Apr 18 18:59:56 2012 +0200
+++ b/Doc/library/weakref.rst	Wed Jun 27 08:23:13 2012 -0700
@@ -24,7 +24,10 @@ by a weak reference.
 A weak reference to an object is not enough to keep the object alive: when the
 only remaining references to a referent are weak references,
 :term:`garbage collection` is free to destroy the referent and reuse its memory
-for something else.  A primary use for weak references is to implement caches or
+for something else.  However, until the object is actually destroyed the weak
+reference may return the object even if there are no strong references to it.
+
+A primary use for weak references is to implement caches or
 mappings holding large objects, where it's desired that a large object not be
 kept alive solely because it appears in a cache or mapping.