I'm not sure if it's a bug as such, but the following
behaviour can be rather annoying if you're playing
around with copy_reg.

On intialisation cPickle creates local copies of the
'dispatch_table', '_extension_registry',
'_extension_cache', and '_inverted_registry'
dictionaries from the copy_reg module.  If that module
is reloaded the dictionaries are reinitialised, and so
out of sync with the copies in the cPickle modules,
which one access from python.

thus the following code results in an Unpicklable
exception.

import cPickle
import copy_reg
reload(copy_reg)
import Numeric
cPickle.dumps(Numeric.array([10,10,01]),1)