Spoke to a supervisor the first time. Called again tonight; same situation. It's a combination of several things: changing airlines, being ultimately an international flight, and not enough time. System just won't book it. So now I'm booked PDX - SEA - PHX - MIA - SXM. Ridiculous. Sigh. At least I'm booked and don't have to spend 12 hours in PHX, but it won't be a fun series of flights.