I would take it back to the LBS and tell them that you need it fixed. It sounds like it's creating a dangerous situation.

Was the LBS able to duplicate the problem during their shakedown run, after they tuned it up for you?

If you're not already dealing with the manager/owner of the LBS, then you need to talk to him/her. If you're already dealing with the manager/owner of the LBS, then you need to have them provide you with the contact info for the Jamis rep.