Functions on statics get chained with duplicate keys?

This logs both `a` and `b`:

``` js
var M = {
  statics: {
    moo: function() { console.log('a'); }
  }
};

var X = React.createClass({
  mixins: [M],
  statics: {
    moo: function() { console.log('b'); }
  },
  render: function(){}
});

X.moo();
```

This seems weird to me and inconsistent with the behavior for non-static functions. Can we change this to give an error too?
