Call model.toJSON always when sync model

backbone.js

@@ -437,7 +437,8 @@
 
     // Return a copy of the model's `attributes` object.
     toJSON: function(options) {
-      return _.clone(this.attributes);
+      options || (options = {});
+      return options.attrs ? options.attrs : _.clone(this.attributes);
     },
 
     // Proxy `Backbone.sync` by default -- but override this if you need
@@ -1573,7 +1574,7 @@
     // Ensure that we have the appropriate request data.
     if (options.data == null && model && (method === 'create' || method === 'update' || method === 'patch')) {
       params.contentType = 'application/json';
-      params.data = JSON.stringify(options.attrs || model.toJSON(options));
+      params.data = JSON.stringify(model.toJSON(options));
     }
 
     // For older servers, emulate JSON by encoding the request into an HTML-form.

test/model.js

@@ -1447,6 +1447,19 @@
     model.save({x: 1}, {wait: true});
   });
 
+  QUnit.test('toJSON is called during save(..., {patch: true})', function(assert) {
+    assert.expect(1);
+    var Model = Backbone.Model.extend({
+      url: '/test',
+      toJSON: function() {
+        assert.strictEqual(this.attributes.x, 1);
+        return _.clone(this.attributes);
+      }
+    });
+    var model = new Model({id: 1});
+    model.save({x: 1}, {patch: true});
+  });
+
   QUnit.test('#2034 - nested set with silent only triggers one change', function(assert) {
     assert.expect(1);
     var model = new Backbone.Model();