This is getting a bit frustrating, wondering if anyone can shed some light. Being part of this alliance is supposed to make things easier, not more difficult.
Since January, I've had 12 instances (all on international flights) where one airline couldn't or wouldn't issue the boarding pass for the other airline (with various different excuses).
Some examples:

1. BKK-ICN (TG) ICN-SEA (OZ) SEA-YVR (AC)
TG couldn't issue any other than own. OZ could only issue it's own. In SEA, had to recheck in with AC. Ticket purchased from TG

2. LAX-SEA (UA) SEA-YVR (AC)
UA didn't issue boarding pass, despite the ticket being purchased on .bomb, with the AC flight as a codeshare. Had to exit security, recheck in at SEA (with UA no less), go through security again?? Neither the AC agent at the gate, nor the RCC would issue the pass.

3. YVR-LHR (AC) LHR-CAI (MS)
AC didn't issue pass, had to get from LHR, despite the MS portion being a AC codeshare, purchased from AC. Was told at YVR that there is no interline agreement with MS! Gimme a break! However, on the return portion, MS issued boarding passes for both legs.

I thought all members in * shared the same platform. So boarding pass should be able to be issued, and the customer shouldn't have to go through these headaches?