Why are my dialog close buttons disabled?

Why are my dialog close buttons disabled?

This is really perplexing.  I'm opening a dialog upon return from an ajax() call, using the returned html as the container.  I've done this before in another application with no problem.  However, in this app, everything works OK with the popup, except that the close button is disabled, and I am not disabling it anywhere in my code.  Here's the call to dialog (in coffeescript):
  1. $.fn.openDialog = ->
      container = $(this[0])
      container.dialog
        autoOpen: true
        height: "auto"
        width: "700px"
        title: container.attr("title")
        modal: false
        close: ->
          $(this).dialog("destroy")
So my ajax calls looks like this:
  1. $(document).on "click", "<whatever selector>", (e) ->
      $.ajax
        url: <the url>
        success: (data, status, xhr) ->
          $(data).openDialog()
And the generated HTML comes out looking like this:
  1. <button  class="ui-button ui-widget ui-state-default ui-corner-all ui-button-disabled ui-state-disabled ui-button-icon-only ui-dialog-titlebar-close"  role="button"  aria-disabled="false"  title="close" >

I've also tried adding "disabled: false" to the dialog call, but it didn't do anything.

Note that it includes the classes ui-button-disabled and ui-state-disabled, but aria-disabled is false.

This is a Rails 3.2 application and the jQuery UI dialog version is 1.10.3