*** Lib/mailbox.py	2007-01-17 15:54:27.000000000 -0500
--- mailbox-unified.py	2007-01-17 15:55:44.000000000 -0500
***************
*** 559,562 ****
--- 559,569 ----
              _lock_file(self._file)
              self._locked = True
+             if self._pending:
+                 warnings.warn("mailbox .lock() method called with pending changes; "
+                               "should have been locked before making changes",
+                               stacklevel=2)
+             else:
+                 # Force re-read of toc to ensure we're up-to-date.
+                 self._toc = None
  
      def unlock(self):