[6.0] CRM - Cannot send multiple times the same attachment through email

Hi,
In Sales->CRM->Leads->Communication&History->Send New Email, you cannot send twice the same attachment because the attachment name (by default filename) must be unique. Moreover, the error message in OpenERP is empty. You need to modify the name of the attachment to something not existing yet.
The attachment name is unique and it should not be the filename but something more complicate that will be unique.

  /home/jbaudoux/OpenERP/preview/src/6.0/server-727263/bin/netsvc.py(489)dispatch()
-> result = ExportService.getService(service_name).dispatch(method, auth, params)
  /home/jbaudoux/OpenERP/preview/src/6.0/server-727263/bin/service/web_services.py(599)dispatch()
-> res = fn(db, uid, *params)
  /home/jbaudoux/OpenERP/preview/src/6.0/server-727263/bin/osv/osv.py(128)wrapper()
-> self.abortResponse(1, inst.name, inst.exc_type, inst.value)
  /home/jbaudoux/OpenERP/preview/src/6.0/server-727263/bin/osv/osv.py(122)wrapper()
-> return f(self, dbname, *args, **kwargs)
  /home/jbaudoux/OpenERP/preview/src/6.0/server-727263/bin/osv/osv.py(176)execute()
-> res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  /home/jbaudoux/OpenERP/preview/src/6.0/server-727263/bin/osv/osv.py(167)execute_cr()
-> return getattr(object, method)(cr, uid, *args, **kw)
  /home/jbaudoux/OpenERP/preview/src/6.0/addons/crm/wizard/crm_send_email.py(148)action_send()
-> references=ref_id or message_id, attach=attach)
  /home/jbaudoux/OpenERP/preview/src/6.0/addons/mail_gateway/mail_gateway.py(131)history()
-> attachments.append(att_obj.create(cr, uid, {'res_model':case._name,'res_id':case.id,'name': att[0], 'datas': base64.encodestring(att[1])}))
> /home/jbaudoux/OpenERP/preview/src/6.0/addons/document/document.py(283)create()
-> raise osv.except_osv(_('ValidateError'), _('File name must be unique!'))