No re-render when changing field choices

In the following example, setting the ChoiceField's choices does not cause a redraw
If I force a redraw, then I see the form correctly displayed.

I expected that setChoices would do a redraw on it's own.

``` javascript
var React = require("react");
var forms = require("newforms");
var IPIN = forms.Form.extend({
device: forms.ChoiceField(),
});
var IPINform = new IPIN();

var Thing = React.createClass({
getInitialState: function(){
return {form: IPINform};
},
forceupdate: function(){
this.forceUpdate();
},
render: function(){
return (


submit

);
}
});

var r = React.render(, document.body);

setTimeout(function(){
IPINform.fields.device.setChoices(["eth0", "eth1"]);
// If I add this, it works:
// r.forceupdate();
}, 100);
```