For some reason, JetBlue.com seems to offer mixed Mint/economy bookings on some routes (for example, SFO-JFK-BTV) but not on others (SFO-FLL-SJU). No luck with the call center, either - they claim it's a "system problem", though that doesn't square with the Burlington example above. I'm told to book separate tickets.

Has anyone else found a workaround, like using a travel agent who can book the legs separately on one PNR?