title: Material-UI + React : Card cannot expand with expander
body: <p>I have a simple Card component that I copied from the material-ui's website.</p>
  
  <p>I'm trying to implement that in my code. When I click on the CardHeader, it would not expand.</p>
  
  <p>This is my Component :</p>
  
  <pre><code>import React, { Component } from 'react';
  import getMuiTheme from 'material-ui/styles/getMuiTheme';
  import MuiThemeProvider from 'material-ui/styles/MuiThemeProvider';
  
  import {Card, CardActions, CardHeader, CardText} from 'material-ui/Card';
  import FlatButton from 'material-ui/FlatButton';
  
  const CardExample = () =&gt; (
      &lt;MuiThemeProvider muiTheme={getMuiTheme()}&gt;
          &lt;Card expanded={true}&gt;
              &lt;CardHeader
                title="Without Avatar"
                subtitle="Subtitle"
                actAsExpander={true}
                showExpandableButton={true}
              /&gt;
              &lt;CardText expandable={true}&gt;
                Lorem ipsum dolor sit amet, consectetur adipiscing elit.
                Donec mattis pretium massa. Aliquam erat volutpat. Nulla facilisi.
                Donec vulputate interdum sollicitudin. Nunc lacinia auctor quam sed pellentesque.
                Aliquam dui mauris, mattis quis lacus id, pellentesque lobortis odio.
              &lt;/CardText&gt;
              &lt;CardActions expandable={true}&gt;
                  &lt;FlatButton label="Action1" /&gt;
                  &lt;FlatButton label="Action2" /&gt;
              &lt;/CardActions&gt;
          &lt;/Card&gt;
      &lt;/MuiThemeProvider&gt;
  )
  
  export default CardExample;
  </code></pre>
  
  <p>And I've imported it to my container here :</p>
  
  <pre><code>import React, { Component } from 'react';
  
  import LogoBig from '../components/logobig';
  import CardExample from '../components/cardexample';
  
  export default class Completed extends Component {
      render() {
          return (
              &lt;div className="popup completed main-container"&gt;
                  &lt;div className="logobar"&gt;
                      &lt;div className="logo"&gt;
                          &lt;LogoBig /&gt;
                      &lt;/div&gt;
                  &lt;/div&gt;
                  &lt;div className="mainpanel"&gt;
                      &lt;CardExample /&gt;
                  &lt;/div&gt;
              &lt;/div&gt;
          );
      }
  }
  </code></pre>
  
  <p>I've implemented it just as the docs in material-ui's site, but the expander does nothing.</p>
  
  <p>Please help me with this. Is there anything wrong with the way I import the component? Or something else?</p>
  
  <p>Thank you</p>