That slow multisort doesn't do multisort at all, generally. If it did, it would be relying on (1) the sort algorithm being stable and (2) the properties being

That slow multisort doesn't do multisort at all, generally. If it did, it would be relying on (1) the sort algorithm being stable and (2) the properties being in the reverse order from what you used in the second multisort algorithm. Eg with properties a,b it sorts on a, then sorts the list again based on b. The list is now in b-order (not a-order) and b-equal blocks are only in a-order if the sort is stable. Meanwhile, the 'fast' algortithm is in a-order with b-ordered a-equal blocks.