watch on array does not work correctly

[xzer]

If we watch to a existing array and then add items to the existing array, the watch function will not work correctly:

  Aj.init(function ($scope) {

    $scope.data = {
      list: []
    };

    $scope.snippet("ul").bind($scope.data, {
      list:{
        _duplicator: "li",
        _item: {
          "nnn": {
            _selector: ".x-watch",
            _watch: {
              _fields: ["name"],
              _cal: function(v){
                console.log("cal", v);
                return v+"-watched";
              }
            },
            _render: function(target, nv, ov, ctx){
              console.log("args", arguments);
              console.log("idx:", ctx.getArrayAssistant().getIndex());
              target.text(nv);
            }
          }
        }
      }
    });

    $scope.data.list.push({
      name: "name-" + i
    });
}

Workaround is to reassign a new array reference to replace the existing array:

    $scope.data.list = Aj.util.clone($scope.data.list);
    $scope.data.list.push({
      name: "name-" + i
    });

[xzer]

Currently, I confirmed that it registered the observer correctly, and the watch result is assigned to the watch result value holder correctly, but the corresponding observer is not invoked.

There may be something I missed or there is a bug in polymer/observe