PAXboy,
Are you sure that neither airline is responsible in that case? Isn't it either the responsibility of the first or final carrier? Or the ticket issuer? I may be wrong and that's just an assumption I've always made. It'd be great if someone had a definitive answer.
As an example, I travelled from PHX, via LAX and LHR to MAN recently and my bag was damaged. AA checked my bags throughout and were the first carrier, BA was the carrier LAX to LHR and BD from LHR to MAN. BA were the ticket issuer. BD only undertook a short leg of the journey but they are the ones who forked out for a new bag and lost gear. I assume there may have been some inter-airline charging going on behind the scenes, or perhaps there's a common pool which they all claim from for this sort of thing. Who knows?
Complicated? Yes.