Amount overpaid vs. amount refunded

What would cause the amount to be refunded (line35a on 1040) to be different from (less than) the amount I overpaid (line 34 on 1040)? It appears that those lines are calculated in TT so I can't change them.  Anyone have any idea how to get this corrected as I would like all the $$ I overpaid to be refunded!  Thanks.