if you remove a friend from a group, the counter by the group didn't change the number of total group members. after deleting a friend while he is in a group. the "add friend" and "add group" buttons are moving to this group, where your ex-friend was. (see picture). page reloading doesn't solve the problem.
after adding the deleted friend again to your friend list, he is again in the group where he was before deleting and the buttons for "add friend" / "add group" are again on their right places.