diff --git a/neutron/db/db_base_plugin_v2.py b/neutron/db/db_base_plugin_v2.py
index d6d4f0352ac..dfcecfb03f5 100644
--- a/neutron/db/db_base_plugin_v2.py
+++ b/neutron/db/db_base_plugin_v2.py
@@ -792,9 +792,11 @@ class NeutronDbPluginV2(db_base_plugin_common.DbBasePluginCommon,
         with context.session.begin(subtransactions=True):
             subnet, changes = self.ipam.update_db_subnet(context, id, s,
                                                          db_pools)
+        # we expire here since ipam may have made changes to relationships
+        # that will be stale on any subsequent lookups while the subnet object
+        # is in the session otherwise.
+        context.session.expire(subnet)
         result = self._make_subnet_dict(subnet, context=context)
-        # Keep up with fields that changed
-        result.update(changes)
 
         if update_ports_needed:
             # Find ports that have not yet been updated
diff --git a/neutron/plugins/ml2/plugin.py b/neutron/plugins/ml2/plugin.py
index 3fa8d9bf9ef..b337af27771 100644
--- a/neutron/plugins/ml2/plugin.py
+++ b/neutron/plugins/ml2/plugin.py
@@ -811,7 +811,7 @@ class Ml2Plugin(db_base_plugin_v2.NeutronDbPluginV2,
             self.type_manager.extend_network_dict_provider(context,
                                                            updated_network)
 
-            updated_network[api.MTU] = self._get_network_mtu(updated_network)
+            updated_network = self.get_network(context, id)
 
             # TODO(QoS): Move out to the extension framework somehow.
             need_network_update_notify = (
@@ -1033,6 +1033,7 @@ class Ml2Plugin(db_base_plugin_v2.NeutronDbPluginV2,
                 context, id, subnet)
             self.extension_manager.process_update_subnet(
                 context, subnet[attributes.SUBNET], updated_subnet)
+            updated_subnet = self.get_subnet(context, id)
             network = self.get_network(context, updated_subnet['network_id'])
             mech_context = driver_context.SubnetContext(
                 self, context, updated_subnet, network,
diff --git a/neutron/tests/tempest/api/test_revisions.py b/neutron/tests/tempest/api/test_revisions.py
index 78fcea4093a..a70b995e3cb 100644
--- a/neutron/tests/tempest/api/test_revisions.py
+++ b/neutron/tests/tempest/api/test_revisions.py
@@ -148,9 +148,7 @@ class TestRevisions(base.BaseAdminNetworkTest, bsg.BaseSecGroupTest):
     @test.requires_ext(extension="dns-integration", service="network")
     def test_update_dns_domain_bumps_revision(self):
         net = self.create_network(dns_domain='example.test.')
-        self.client.update_network(net['id'], dns_domain='exa.test.')
-        # TODO(kevinbenton): use update result after bug/1627628 is fixed
-        updated = self.client.show_network(net['id'])
+        updated = self.client.update_network(net['id'], dns_domain='exa.test.')
         self.assertGreater(updated['network']['revision_number'],
                            net['revision_number'])
         port = self.create_port(net)
@@ -198,13 +196,12 @@ class TestRevisions(base.BaseAdminNetworkTest, bsg.BaseSecGroupTest):
     @test.requires_ext(extension="port-security", service="network")
     def test_update_port_security_bumps_revisions(self):
         net = self.create_network(port_security_enabled=False)
-        self.client.update_network(net['id'], port_security_enabled=True)
-        # TODO(kevinbenton): use update result after bug/1627628 is fixed
-        updated = self.client.show_network(net['id'])
+        updated = self.client.update_network(net['id'],
+                                             port_security_enabled=True)
         self.assertGreater(updated['network']['revision_number'],
                            net['revision_number'])
-        self.client.update_network(net['id'], port_security_enabled=False)
-        updated2 = self.client.show_network(net['id'])
+        updated2 = self.client.update_network(net['id'],
+                                              port_security_enabled=False)
         self.assertGreater(updated2['network']['revision_number'],
                            updated['network']['revision_number'])
         port = self.create_port(net, port_security_enabled=False)