You’ve got to both respect Automattic for releasing their internal code as open source while also giving them a break for not assuring that it works for anybody else. One of their projects, the WordPress.com Video Server is a sophisticated WordPress plugin that handles video transcoding and offers a bit of a YouTube in a box solution for WordPress.
The bug I found is that the code assumes WPMU is running in subdomain mode, rather than subdirectory mode. This assumption causes an ajax request to go to the wrong URL and return the wrong data. The patch simply applies WordPress’ plugins_url() function that debuted in 2.6.