I booked a flight from IAD to South Africa for November. UA flights and SAA flights. Booked in S on UA and L on SAA which should both earn miles on UA MP. Was able to see the UA fare classes before buying but only saw the SAA fare class once it posted on my united.com page.

There was a schedule change on a UA flight which changed my layover in LHR to 45min which wasn't legal or plausible at all. As mentioned, UA can't change the ticket but called Vayama and only took them 15 minutes to change me to a later UA flight I preferred. There was no S fare available on the next flight so they booked me in W.

Hope this helps.