Zope External Method + xmlrpclib

zope 2.13.22
Python 2.7
Plone 4.3

Pythonscript on local filesystem
---------------------------------
import xmlrpclib
target='http://localhost:8080/test'
xmlrpclib.Server(target).scripts.setEmail('29999','info@example.org')

...works as expected -> mail address changed but

target='http://admin:pw@localhost:8080/test'
... does not work -> no error, mail address does not change

External Method "setEmail.py":
-----------------
from Products.CMFCore.utils import getToolByName

def setEmail(self,userID,mail):
    mt = getToolByName(self, 'portal_membership')
    member = mt.getMemberById(userID)
    member.setMemberProperties(mapping={'email': mail})