Once you have manually repositioned a pinned icon the entire list at that time will be assigned positions as this is required in order to maintain the positions requested.
To revert back to A-z sorting you need to delete the entries here in the registry and sign out and in again.
HKEY_CURRENT_USER\SOFTWARE\Stardock\Start8\Start8.ini\Pinned
If you manually reorder the pinned items the order will be forced again and new items will appear at the bottom.
