subprocess.Popen.__exit__ doesn't wait for process end

Doc/library/subprocess.rst

 :mod:`subprocess` --- Subprocess management
 ===========================================
 
 .. module:: subprocess
    :synopsis: Subprocess management.
 .. moduleauthor:: Peter Åstrand <astrand@lysator.liu.se>
 .. sectionauthor:: Peter Åstrand <astrand@lysator.liu.se>
 
 
 The :mod:`subprocess` module allows you to spawn new processes, connect to their
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       This feature is only available if Python is built with universal newline
       support (the default).  Also, the newlines attribute of the file objects
       :attr:`stdout`, :attr:`stdin` and :attr:`stderr` are not updated by the
       :meth:`communicate` method.
 
    If given, *startupinfo* will be a :class:`STARTUPINFO` object, which is
    passed to the underlying ``CreateProcess`` function.
    *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.
 
 
 .. data:: DEVNULL
 
    Special value that can be used as the *stdin*, *stdout* or *stderr* argument
    to :class:`Popen` and indicates that the special file :data:`os.devnull`
    will be used.
 
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 4. Backslashes are interpreted literally, unless they
    immediately precede a double quotation mark.
 
 5. If backslashes immediately precede a double quotation mark,
    every pair of backslashes is interpreted as a literal
    backslash.  If the number of backslashes is odd, the last
    backslash escapes the next double quotation mark as
    described in rule 3.