Unable to set virtual machine custom compatibilty version using python SDK

Issue

Unable to change 'custom_compatibility_version' virtual machine's attribute using 'ovirt-engine-sdk-python'.

Execute the following script to change 'custom_compatibilty_version' attribute from 'myvm' virtual machine:

#! /usr/bin/python
# -*- coding: utf-8 -*-

from time import sleep, gmtime, strftime
from ovirtsdk.api import API
from ovirtsdk.xml import params
from ovirtsdk.infrastructure.errors import RequestError, ConnectionError


RHEV_URL = "https://rhvm.example.com/ovirt-engine/api"
RHEV_USERNAME = "admin@internal"
RHEV_PASSWORD = "******"


if __name__ == '__main__':

      api = API(url=RHEV_URL,
        username=RHEV_USERNAME,
        password=RHEV_PASSWORD,
        ca_file="rhvm-ca.pem", debug=True)

      vm = api.vms.get(name = 'myvm')
      version = params.Version(major=4, minor=1)
      #version = None
      vm.custom_compatibility_version = version
      try:
        vm.update()
        print "VM Updated"
      except RequestError as ex:
        print "Unexpected error: %s" % ex
        pass

The script finishes with no error but the VM's 'custom_compatibility_version' attribute is not changed.