When I worked on the ground with EI way back in 99 we were told it was OK to interline bags with two seperate tickets. Then in 2000 we were told that we should not really do it. Then in 2001 we were told under no circumstances must we do it. By this stage I was working in customer relations in the baggage claims section and I realised why.
Basically it is up to the final carrier of travel to settle a claim for damaged or missing luggage which sounds fair enough. However, why should an airline accept responsibility for another airlines actions when it should not have been done? On a normal interline ticket the airline settleing the claim can prorate the other airline or airlines part of the cost of the claim but apparently when two tickets are involved, the airline being prorated do not legally have to pay anything!!!