title: Backspace key not working on jQuery UI Dialog input
body: <p>I have a jQuery UI Dialog with a form inside it. When I show the page, I set the focus on the first input of the form. </p>
  
  <p>If I type some text, the input shows it, but if I press Backspace or Tab key, this keys don't work: Backspace doesn't delete content of the input field and Tab  doesn't focus on the next tabindex element.</p>
  
  <p>However, if I click first on the dialog title bar, these keys now work.</p>
  
  <p>I'm using Backbone views to show the DOM but I don't think this is causing the issue.</p>
  
  <p>I test to change form and input fields CSS z-index property to a very high value but this doesn't work. Any idea?</p>
  
  <p>EDIT: the problem only happens when two jQuery UI dialogs are visible. If only the dialog with the form is visible backspace and tab work, but I can't figure out how to solve it</p>