drupe automatically populates the Favorites view with a special blend of contacts you connect with frequently. This is drupe's Contact Suggestion feature.
You can tell the suggested contacts from the contacts you have starred by the little star above the avatars of the latter.
When you try to reorganize your favorites by dragging and dropping, you won't be able to place a starred contact in the suggested contacts' section at the bottom of the favorites list.
To disable the Contact Suggestion, go to drupe settings > uncheck Contact Suggestion.