[Zope-CMF] manage_afterAdd not being called?

[seb bacon]

I'm adding some content to a folder like so:

   f = portal_membership.getHomeFolder(member_id)
   f.invokeFactory('MailMessage',id)
   o = f._getOb(id)
   o.edit(file)

But it's not getting indexed, which I presume is because
manage_afterAdd isn't getting called.  Can anyone tell me why this is?
Should I be creating the content in a different way?

Cheers,

seb