dont send the key to the server, we didn't do that before this feature, and we do not have a good way to ensure the right keys in compositions.

src/Umbraco.Web.UI.Client/src/common/services/umbdataformatter.service.js

@@ -75,7 +75,7 @@
                 });
                 saveModel.groups = _.map(realGroups, function (g) {
 
-                    var saveGroup = _.pick(g, 'inherited', 'id', 'sortOrder', 'name', 'key', 'alias', 'type');
+                    var saveGroup = _.pick(g, 'inherited', 'id', 'sortOrder', 'name', 'alias', 'type');
 
                     var realProperties = _.reject(g.properties, function (p) {
                         //do not include these properties