The container={mountNode} is a bit mysterious in the popover documentation. I see where it's defined in the docs:

 executeCode: function() {
    var mountNode = this.refs.mount.getDOMNode();

But which node it should reference is hard to decipher. I've tried

  componentDidMount: function() {
    var mountNode = this.refs.button.getDOMNode()
}

With no luck (it's still positioned incorrectly). A little bit of documentation of what this node should refer to and how to access it would be really helpful.