Detail elements in a detail group move as a unit with respect to draw order. They move forward or backward together when the group draw order is changed. If you want to change the draw order of individual members of the group, you first need to edit the group. After you change the draw order of the members of a detail group and finish editing the group, all instances of that detail group are updated with the new draw order.
For more information on draw order, see Sorting the Draw Order of Detail Components.