Originally Posted by
exwannabe
You are certainly correct here.
Is it possible that the EWR-SMF return was pricing with a fare break thus violating the"2 fare component" rule on the outbound fare?
After some further deep digging on ITA this is indeed the right explanation. EWR to SMF is not pricing as a through fare for some reason, instead breaking at MSP or ATL. It's a little strange but at least it's an explanation that sort of makes sense.