diff -r 482f60d6a687 Doc/library/subprocess.rst
--- a/Doc/library/subprocess.rst	Wed May 11 22:37:50 2011 +0800
+++ b/Doc/library/subprocess.rst	Wed May 11 18:35:39 2011 +0200
@@ -219,13 +219,19 @@
    *creationflags*, if given, can be :data:`CREATE_NEW_CONSOLE` or
    :data:`CREATE_NEW_PROCESS_GROUP`. (Windows only)
 
-   Popen objects are supported as context managers via the :keyword:`with` statement,
-   closing any open file descriptors on exit.
+   Popen objects are supported as context managers via the :keyword:`with` statement:
+   on exit, standard file descriptors are closed, and the process is waited for.
    ::
 
       with Popen(["ifconfig"], stdout=PIPE) as proc:
           log.write(proc.stdout.read())
 
+   .. note::
+
+      In the initial implementation, the process was not automatically waited
+      for upon exit from the context manager. Code intending to be compatible
+      with Python 2.7.1 and earlier should explicitly call :meth:`Popen.wait`.
+
    .. versionchanged:: 3.2
       Added context manager support.
 
diff -r 482f60d6a687 Lib/subprocess.py
--- a/Lib/subprocess.py	Wed May 11 22:37:50 2011 +0800
+++ b/Lib/subprocess.py	Wed May 11 18:35:39 2011 +0200
@@ -796,6 +796,8 @@
             self.stderr.close()
         if self.stdin:
             self.stdin.close()
+        # Wait for the process to terminate, to avoid zombies.
+        self.wait()
 
     def __del__(self, _maxsize=sys.maxsize, _active=_active):
         if not self._child_created:
diff -r 482f60d6a687 Lib/test/test_subprocess.py
--- a/Lib/test/test_subprocess.py	Wed May 11 22:37:50 2011 +0800
+++ b/Lib/test/test_subprocess.py	Wed May 11 18:35:39 2011 +0200
@@ -1590,7 +1590,8 @@
     def test_returncode(self):
         with subprocess.Popen([sys.executable, "-c",
                                "import sys; sys.exit(100)"]) as proc:
-            proc.wait()
+            pass
+        # __exit__ calls wait(), so the returncode should be set
         self.assertEqual(proc.returncode, 100)
 
     def test_communicate_stdin(self):