Maybe a similar experience. In late Nov., when I was on a oneworld Explorer trip, I had a CP codeshare operated by BA, LHR-YYZ, connecting to YYZ-YOW on CP, the same day connection.

BA could not check me in through YOW at the check-in counter. They told me that I may be able to get a boarding pass for YYZ-YOW at the gate before my LHR-YYZ flight. (She seems to have called CP to make that arrangement.) I didn't bother partly because it was one of those flights that I had different FFP account numbers registered.

At the end of the day, I just asked for LHR-YYZ ony and I re-checked in at YYZ.

(The BA staff at the counter also did not recognise my Asiamiles (CX) card, so she picked up a thick manual (maybe 300 pages) on the desk to check which card it was. She was laughing that there were so many cards to remember. I laughted as well.)

Just this weekend, I had oneworld flights -- TPE-HKG on CX and then HKG-SIN-CGK on QF. At TPE, CX gave me boarding passes for TPE-HKG-SIN. The two boardng passes were CX plates. Up to two sectors they can issue, they told me.

When I went to the gate in HKG, I was given QF plate boarding passes for HKG-SIN-CGK. They were there when I went to the gate. So I didn't check in myself for SIN-CGK.

Well, for this weekend trip, I thought having an alliance would not be bad.