[Zope] Proxy role doesn't work for manage_clone?

[Hamish Lawson]

I have a Python Script that contains a line like this (with 
appropriate assignments of DestinationFolder, PrototypeObject and 
folder_id):

    DestinationFolder.manage_clone(PrototypeObject, folder_id)

The script is intended to be run by anonymous users, but only the 
Manager role has permission to add folders to DestinationFolder (the 
folder acquires its permission settings ultimately from the root 
folder, which specifies that the Manager role has all permissions). 
So I gave the script a proxy role of Manager. Despite this Zope still 
prompts for authentication credentials. Why doesn't the proxy role 
seem to be taking effect (another test script has successfully 
established that the Anonymous User can read the properties of 
PrototypeObject, in case that was an issue).

Hamish Lawson