It is the standard practice that where there may be some doubt about the correctness of an appeal tribunal's decision, a special team of decision makers will examine the decision and ask for a statement of reasons for the decision, with a view to appeal.
Cases of this kind are relatively rare however, as there can only be an appeal to the Upper Tribunal on a point of law, and as it costs the DWP in excess of £2,000 to appeal to the UT, they have to be sure that there is a more than reasonable chance that the appeal will succeed.
Congratulations on your DLA award and enjoy the arrears at your leisure.
Nothing on this board constitutes legal advice - always consult a professional about specific problems