It is not possible to re-order the steps defined for "Before release build" and for "After successful release build" or "After failed release build".

I tried on Firefox, Chrome and IE; in all cases the step that's being dragged is moved to the top of the window immediately then comes back to its initial position when the user releases the mouse button. The only way to insert a step is to actually delete ALL the steps and add them again in the proper sequence. Very annoying.