auto_javascript_include_tag fails when directory_indexes is active

Middleman Bug Demo

middleman init example.com
cd source
cp index.html.erb example.html.erb
edit example.html.erb to

---
title: Example Page
---
<h1>Example Page</h1>
<p>Hello, world!</p>

echo 'alert("Here is an alert.");' > /javascripts/example.js

edit javascripts/all.js
delete the line "//= require_tree .”
  This keeps middleman from walking the /javascripts directory and compiling our test into one all.js file

edit layouts/layout.erb
add  <%= auto_javascript_include_tag %>, before </head>, about line 14

edit ../config.rb
remove the comment on line 40, enabling "   activate :livereload”

middleman server

visit http://localhost:4567/
  The default page only should display. No javascript should display. 
visit http://localhost:4567/example.html
  An alert should display with the example page

edit ../config.rb
add activate :directory_indexes

visit http://localhost:4567/example/
  The alert will not display. Check the page source, example.js is not included.