dojo bug - ContentPane does not expand

dojo bug - ContentPane does not expand

HTML

<link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/dojo/1.10.0/dijit/themes/claro/claro.css">
<div id="contentPanel">
  <div id="titlePanel">
    <div id="button">
    </div>
    <div id="content">
    </div>
  </div>
</div>

CSS

#titlePanel {
  height: auto !important;
}

JavaScript

require(["dijit/layout/ContentPane", "dijit/TitlePane", "dijit/form/Button", "dojo/domReady!"], function(ContentPane, TitlePane, Button) {
  this._contentPanel = new ContentPane({
    style: "background-color:red;"
  }, "contentPanel");

  this._titlePanel = new TitlePane({
    title: "I'm a TitlePane",
    content: "Collapse me!"
  }, "titlePanel");

  this._button = new Button({
    label: "Click me many times!",
    onClick: function() {
      this._titlePanel.addChild(new Button({
        label: "Test",
        style: "width: 250px"
      }));
    }.bind(this)
  }, "button");

  this._contentPanel.addChild(this._titlePanel);
  this._titlePanel.addChild(this._button);
  this._contentPanel.startup();
});