I saw something kind of similar last year, where JetBlue.com was selling SJU-STX on a codeshare carrier (Cape Air) for something like $229. But if you searched Kayak.com you could find the same JetBlue codeshare flight for $89, and the Kayak link would lead to JetBlue.com where you could book at the lower price. Very odd. Not the same thing, but it just shows that JetBlue's website doesn't always sync with other websites.

If the Expedia flights you're seeing are what you want, I'd say try booking them. Then you can call JetBlue to confirm that the reservation is valid. That said, I'm fairly certain there is no nonstop from BDL-SXM.