Here's an odd one, at least to me, but the airline world is a web of rules...

Tried to ticket EZE-SCL-LAX for the return of a J award on LAN. SCL has no U seats right now, but there are plenty of U seats for EZE-LIM-LAX on LP. Reservation goes through, I get my seats, etc.

This morning, AA phones me to say that LP isn't allowing my journey, as it contains an LP transit in LIM. The agent said I could only transit LP to LP at LIM if I'm on a through flight, which is the one-stop Sao Paulo-LAX.

I could fly EZE-Sao Paulo-LIM-LAX, but that'd cause me to leave EZE much earlier than I'd planned.. so for now, I'll just take the Y seat SCL-LAX and hope LA releases a U seat sometime over the next month. (Unless I have slim chances on this route).