When you choose a script file for your ADT, its code should load into the editor.
Steps to reproduce:
1. Admin -> Site Administration -> Configuration -> Application Display Templates
2. Add -> Blogs Template ... to bring up template editor
3. Choose an existing .ftl file.
Example contents could be ...
Here are the titles of the blog entries:
<#list entries as curBlogEntry>
The code should show in the editor, but it does not. See attached screenshot.
If the user clicks save, the file's code persists to the template; but the user doesn't know that. He must re-open the template in the editor to confirm that it persisted. Alternatively, he can also click save-and-continue to get the code to appear and continue to work on it.