Ember - HTML5 Drag and Drop div containing a div

Quite simply, I seem to have HTML5 Drag and Drop working in an Ember app, but it doesn't seem to work when a draggable div contains another div. Any ideas appreciated.

eg This works:

<div draggable="true">
    <h1>Drag</h1>
    <h2>Me!</h2>
</div>

This doesn't.

<div draggable="true">
    <div>
        <h1>Drag</h1>
        <h2>Me!</h2>
    </div>
</div>