A great example is UA924 on Monday Jan 28 from IAD to LHR. It shows PN9, PZ0, IN9. UA reservations on the phone said they "see" PZ9 too and were alarmed to hear web showed PZ0. I tried booking a flight with GPU to clear into business immediately and it showed as "not available."
If this glitch is true, it likely screwed me out of my upgrade this week. Mad.