Pickling errors with tz.FixedOffsetTimezone

I have a web application that uses memcached to store some data.
Some of that data is retrieved through psycopg2 (2.0.8) and contains
datetime instances.

Sometimes I get the following exception while trying to put objects
into the memcached cache:
"PicklingError: Can't pickle <class
'psycopg2.tz.FixedOffsetTimezone'>: it's not the same object as
psycopg2.tz.FixedOffsetTimezone"

I googled it and the only result I got is from a thread in the Django
mailing list confirming my suspicions.

It seems there's some identity problem with the class associated to
the datetime pickled instance.

I read the source code of the pickle module
<http://svn.python.org/view/python/trunk/Lib/pickle.py?view=markup>
and I found the place where the exception is raised in the save_global() method:

"""
    def save_global(self, obj, name=None, pack=struct.pack):
        write = self.write
        memo = self.memo

        if name is None:
            name = obj.__name__

        module = getattr(obj, "__module__", None)
        if module is None:
            module = whichmodule(obj, name)

        try:
            __import__(module)
            mod = sys.modules[module]
            klass = getattr(mod, name)
        except (ImportError, KeyError, AttributeError):
            raise PicklingError(
                "Can't pickle %r: it's not found as %s.%s" %
                (obj, module, name))
        else:
            if klass is not obj:
                raise PicklingError(
                    "Can't pickle %r: it's not the same object as %s.%s" %
                    (obj, module, name))

        ...
"""

whichmodule() basically looks for the module in sys.module but if the
class is not the same
it refuses to pickle.

Any ideas? It's a very strange error

-- 
Lawrence, http://oluyede.org - http://twitter.com/lawrenceoluyede
"It is difficult to get a man to understand
something when his salary depends on not
understanding it" - Upton Sinclair