Patch from Joe Eaton <jeaton@hostway.net> (SF#100741) to fix following problem:

There is a silly bug in the fall-back dumbdbm.py database package in
  the Python 1.5.2 standard distro. This bug causes any changes to an
  existing item to generate a new key, even when the key already
  exists.  After many updates, the .dir file used by dumbdbm grows to
  a huge size, and can cause filesystem problems.

Lib/dumbdbm.py

@@ -120,7 +120,6 @@ class _Database:
 			else:
 				pos, siz = self._addval(val)
 				self._index[key] = pos, siz
-			self._addkey(key, (pos, siz))
 	
 	def __delitem__(self, key):
 		del self._index[key]