I believe in instances like this where same day travel is involved (eg: Oct 25 MXP-SFO, SFO-SYD) the computer will order flights in ascending flight number sequence (thus your 863 SFO-SYD is a lower flight # than the 9xx for MXP-SFO)... thus, the transpac credits before the transatlantic. This is what I have noticed over the years, anyway.

ie: the computer is sometimes a dumbass about actual routings.

I agree, I'd keep quiet and just let it credit that way - after all you earned a few bonus miles you wouldn't have got if the order had gone the other way.

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RichardMEL, UA 1K
A Star Alliance Member.