So in advance search you were specifically putting in W and it is still coming back with K/S?
I've always found UA to be pretty decent with o/w tickets. I've booked and GPUd one ways on MEL-LAX x 2, SFO-NRT, LHR-EWR x 2, EWR-HKG, SFO-HKG without any seemingly inflated cost.
Did you try calling in and booking with a agent?