title: Context Menu not reflecting check/uncheck on click
body: <p>I have a context menu on click of a button. There are 3 items which are initially checked. On click of each item, I am toggling the check. The check/uncheck is not reflecting while the context menu is open. This used to work earlier but with the latest react versions it looks to be broken.</p>
  
  <p>The snippet is here </p>
  
  <pre><code>import { initializeIcons } from '@uifabric/icons';
  import { DefaultButton, IContextualMenuItem, IContextualMenuProps, IContextualMenuStyles } from 'office-ui-fabric-react';
  import React from 'react';
  initializeIcons();
  
  //Without this style defined, check/uncheck will not reflect in UI.
  const cmStyles:Partial&lt;IContextualMenuStyles&gt; = {
      title:{},
      header:{},
      list:{
      },
      root:{
      },
      subComponentStyles:{
          callout:{
              root:{
              }
          },
          menuItem:{}
      },
      container:{
      }
  }
  
  const keys: string[] = [
      'Item1',
      'Item2',
      'Item3'
  ];
  
  interface IState {
      updateUI: boolean;
  }
  
  export default class ContextMenuCheck extends React.Component&lt;{}, IState&gt;{
      state:IState = {
          updateUI: false
      }
  
      constructor(props:any){
          super(props);
      }
  
      onTogglePlanType = (ev?: React.MouseEvent&lt;HTMLElement&gt; | React.KeyboardEvent&lt;HTMLElement&gt;, item?: IContextualMenuItem):void =&gt; {
          ev &amp;&amp; ev.preventDefault();//This will not close the menu
          item.checked = !item.checked;
          this.setState({updateUI:true});
      };
  
      menuItems: IContextualMenuItem[] = [
          {
            key: keys[0],
            text: keys[0],
            canCheck: true,
            checked: true,
            onClick: this.onTogglePlanType
          },
          {
            key: keys[1],
            text: keys[1],
            canCheck: true,
            checked: true,
            onClick: this.onTogglePlanType
          },
          {
            key: keys[2],
            text: keys[2],
            canCheck: true,
            checked: true,
            onClick: this.onTogglePlanType
          }
      ];
  
      menuProps: IContextualMenuProps = {
          items:this.menuItems,
          styles: cmStyles
      };
  
      componentDidMount() {
      }
  
      render() {
          return (
          &lt;DefaultButton text="Click Me"  menuProps={this.menuProps}/&gt;
          );
      }
  }
  
  ReactDOM.render(
    &lt;ContextMenuCheck /&gt;, 
    document.getElementById("content")
  );
  
  </code></pre>