I think I know why the faces disappeared... Since I had to create a new Usergroup for this, the user ranks were lost for those members with equal to or more than 2500 posts (plus date/reputation criteria). I'm not sure how I'm going to solve this problem because I can give everyone the normal 2500+ face, however, I think I would need to create a new Usergroup for each custom face. Maybe just a rank, or maybe I can use HTML in the user title to insert an image... I'm not entirely sure (if you haven't already noticed) but I'll experiement.
I'm going to check on the alleged -2,500 post users having the ability to use custom titles.
In the mean time, hold tight
I didn't find any member in the new usergroup that did not have over 2,500 posts... If you could point out a user that has less than the required posts but has a custom title, I'll take a look.