Threaded Comments Issues

I have been unable to get the threaded comments functionality to work properly on the following site:

http://arkansashealthcareers.com

I can check the markup with FireBug and it is dynamically updating the hidden input fields properly when I hit the reply button, but then once the comments are approved and posted, they aren’t nested in child lists of the corresponding parent comment.

Anybody have any thoughts as to what could be causing this? As a caveat, I am technically using WPMU 2.9.1 with BuddyPress.