You can get these tiny fare amounts attributed to the short legs. Early last year I flew LHR to LAX, with a connection in PHX on the return. (This was a BE fare and the PHX stop was to lock in a SWU). Back calculating from the LPs, the outbound fare was $146, the return was $12 (to PHX) and $311 (PHX to LHR). I've also had a domestic US flight with connection split $71/$8.