Unread thread links after top-level category deployment

Hello all,

 

We've had a link on our forums for some time, which takes you to a list of unread threads.  Our superusers like it.  :)

 

http://discussions.tomtom.com/t5/forums/recentpostspage/category-id/en_en/post-type/thread

 

Last night we deployed a new multi-language setup using top-level categories.  Since it went live, the above link seems to simply show a complete list of threads, whether they've been viewed or not.

 

Does anyone know what's causing it?

 

Thanks!