Most of the cases (55) where SPTO outperforms SO are cases where SPTO knows that a phrase pair contains the desired reordering, but SO does not.
sO has to use an external reordering which brings poorer translation than the internal reordering, because the words are translated individually rather than by a single phrase (37 cases), or it has to reject the desired reordering (18 cases), which also hurts translation, since it does not get the correct word order.