The other thing to watch out for with SQ fares is that if any one of your legs is in a non mileage earning class then the whole ittinerary is non-mileage earning. So one G fare class flight from say SIN to KUL can wipe out all of the other flights even if they were booked in F.

I am however, unsure if the mileage wipe continues on to other airlines if you are crediting the miles to anyone but SQ. so you might get UA miles on a UA flight, but not on any SQ flights in that ittinerary.