diff -r 8319db2dd342 Lib/mailbox.py
--- a/Lib/mailbox.py	Fri Jun 17 22:24:05 2011 -0400
+++ b/Lib/mailbox.py	Mon Sep 19 03:19:05 2011 -0700
@@ -1467,8 +1467,7 @@ class Message(email.message.Message):
 
     def _become_message(self, message):
         """Assume the non-format-specific state of message."""
-        for name in ('_headers', '_unixfrom', '_payload', '_charset',
-                     'preamble', 'epilogue', 'defects', '_default_type'):
+        for name in message.__dict__:
             self.__dict__[name] = message.__dict__[name]
 
     def _explain_to(self, message):
@@ -1584,7 +1583,9 @@ class MaildirMessage(Message):
         else:
             raise TypeError('Cannot convert to specified type: %s' %
                             type(message))
-
+        del message['_subdir'] 
+        del message['_info'] 
+        del message['_date'] 
 
 class _mboxMMDFMessage(Message):
     """Message with mbox- or MMDF-specific properties."""
@@ -1695,6 +1696,7 @@ class _mboxMMDFMessage(Message):
         else:
             raise TypeError('Cannot convert to specified type: %s' %
                             type(message))
+        del message['_from'] 
 
 
 class mboxMessage(_mboxMMDFMessage):
@@ -1769,6 +1771,7 @@ class MHMessage(Message):
         else:
             raise TypeError('Cannot convert to specified type: %s' %
                             type(message))
+        del message['_sequences'] 
 
 
 class BabylMessage(Message):
@@ -1862,6 +1865,8 @@ class BabylMessage(Message):
         else:
             raise TypeError('Cannot convert to specified type: %s' %
                             type(message))
+        del message['_labels'] 
+        del message['_visible'] 
 
 
 class MMDFMessage(_mboxMMDFMessage):