mid-last year I booked an international trip over the phone and told the agent the flight numbers I wanted and she booked 917 FRA-IAD-SEA as separate segments for me at my request...no problem. But then later I called because I was having trouble changing seats online and the agent I talked to told me it should not have been booked as 2 segments...but he said he'd leave it as is for that trip but in the future I should book it as one segment because they were told it screws up inventory management (or something like that). Whatever. I also use multi-city as much as possible to avoid this foolishness.