Directory Feature Image Broken

Cannot set listing feature image in frontend.
Button opens file browser, but nothing happens after selection (no network activity, etc).
The content 'Add Media' button still works fine however.

Clean WordPress 3.5.1 install using FTP (ALL settings default, Permalink: Post name, Twenty Twelve theme)
WPMU directory 2.2.3 uploaded ZIP thru WP (with its builtin CustomPress)
Listings: Settings: Capabilities: Administrator: ALL ticked
Windows offline, Linux online, same deal.

JS error:
js_translate is not defined.

The code:
<script type="text/javascript">js_translate.image_chosen = 'Feature Image Chosen';</script>

Line 88:

Line 95: