Launchpad itself

 diff --git a/lib/lp/code/model/branch.py b/lib/lp/code/model/branch.py
 index 452bf4e..c9a98cd 100644
 --- a/lib/lp/code/model/branch.py
 +++ b/lib/lp/code/model/branch.py
@@ -689,7 +689,9 @@ class Branch(SQLBase, WebhookTargetMixin, BzrIdentityMixin):
              self,
              check_permissions=False)
          for snap in snaps:
--            snap.is_stale = True
++            # ISnapSet.findByBranch returns security-proxied Snap objects on
++            # which the is_stale attribute is read-only.  Bypass this.
++            removeSecurityProxy(snap).is_stale = True
      def addToLaunchBag(self, launchbag):
          """See `IBranch`."""
 diff --git a/lib/lp/snappy/browser/snap.py b/lib/lp/snappy/browser/snap.py
 index ac7925c..c7b0ea3 100644
 --- a/lib/lp/snappy/browser/snap.py
 +++ b/lib/lp/snappy/browser/snap.py
@@ -835,6 +835,10 @@ class BaseSnapEditView(SnapAuthorizeMixin, SnapInformationTypeMixin,
              if 'store_channels' in data:
                  del data['store_channels']
          need_store_reauth = self._needStoreReauth(data)
++        info_type = data.get('information_type')
++        if info_type and info_type != self.context.information_type:
++            self.context.information_type = info_type
++            del data['information_type']
          self.updateContextFromData(data)
          if need_store_reauth:
              self.requestAuthorization(self.context)
 diff --git a/lib/lp/snappy/browser/tests/test_snap.py b/lib/lp/snappy/browser/tests/test_snap.py
 index 486e586..8a96e17 100644
 --- a/lib/lp/snappy/browser/tests/test_snap.py
 +++ b/lib/lp/snappy/browser/tests/test_snap.py
@@ -1150,6 +1150,35 @@ class TestSnapEditView(BaseTestSnapView):
              "A public snap cannot have a private owner.",
              extract_text(find_tags_by_class(browser.contents, "message")[1]))
++    def test_edit_public_snap_make_private_in_one_go(self):
++        # Move a public snap to a private owner and mark it private in one go
++        series = self.factory.makeUbuntuDistroSeries()
++        with admin_logged_in():
++            snappy_series = self.factory.makeSnappySeries(
++                usable_distro_series=[series])
++        login_person(self.person)
++        private_project = self.factory.makeProduct(
++            name='private-project',
++            owner=self.person, registrant=self.person,
++            information_type=InformationType.PROPRIETARY,
++            branch_sharing_policy=BranchSharingPolicy.PROPRIETARY)
++        snap = self.factory.makeSnap(
++            registrant=self.person, owner=self.person, distroseries=series,
++            store_series=snappy_series, project=private_project)
++        private_team = self.factory.makeTeam(
++            owner=self.person, visibility=PersonVisibility.PRIVATE)
++        private_team_name = private_team.name
++
++        browser = self.getViewBrowser(snap, user=self.person)
++        browser.getLink("Edit snap package").click()
++        browser.getControl("Owner").value = [private_team_name]
++        browser.getControl(name="field.information_type").value = (
++            "PROPRIETARY")
++        browser.getControl("Update snap package").click()
++
++        login_admin()
++        self.assertEqual(InformationType.PROPRIETARY, snap.information_type)
++
      def test_edit_public_snap_private_branch(self):
          series = self.factory.makeUbuntuDistroSeries()
          with admin_logged_in():