Cannot use ~user/+subscriptions to unsubscribe from dupes of private bugs

I hoped that the new subscriptions page would permit me to remove the Registry admins from bug subscriptions (https://launchpad.net/~registry/+subscriptions). I can use the form linked from the page, but the action fails because of duplicates

super(BugSubscriptionSubscribeSelfView, self).initialize()
Module canonical.launchpad.webapp.launchpadform, line 126, in initialize
self.form_result = action.success(data)
Module zope.formlib.form, line 606, in success
return self.success_handler(self.form, self, data)
Module lp.bugs.browser.bugsubscription, line 352, in subscribe_action
self._handleUnsubscribe(subscription_person)
Module lp.bugs.browser.bugsubscription, line 366, in _handleUnsubscribe
self._handleUnsubscribeOtherUser(user)
Module lp.bugs.browser.bugsubscription, line 406, in _handleUnsubscribeOtherUser
self._getUnsubscribeNotification(user, unsubed_dupes)))
Module lp.bugs.browser.bugsubscription, line 425, in _getUnsubscribeNotification
unsubed_dupes)
Module lp.bugs.browser.bugsubscription, line 460, in _getUnsubscribedDupesMsgFragment
canonical_url(unsubed_dupe), unsubed_dupe.title,
Unauthorized: (<Bug at 0xf086d50>, 'title', 'launchpad.View')