From the Model Mayhem FAQ:

How come some users/casting calls look older or are on top of newer users or casting calls?
One of the benefits of being a VIP and Premium member is receiving preferred placement on results pages - meaning VIP and Premium members and their posts will be pinned on top of basic users in Browse and Casting Call search pages.

This may mean that from time to time, subscribing users who have not been active for a while or who have posted older casting calls may appear on top of newer users or castings. If you are searching for the newest content, you will simply need to keep scrolling past the VIP and Premium users to the free user section.