AJAX won't refresh on Activity page for non-logged in users

I would like to allow new and unregistered users access to the Activity page, just not post updates. I think that's how I have it setup. However in Blogs MU, when a non-logged in user selects the dropdown to change from All Activity to Posts or Comments the screen blanks but never redraws. The user has to manually refresh the page.

It works perfectly for logged in users.

Is there some setting that needs to be changed to allow this to work?