OK - I figured it out (not that it took all that much figuring). Two wires from the power window control on the driver's door had split inside the rubber boot at the driver's door hinge. A bit of splicing and electrical tape solved the problem. In a way this is just like the tailgate wire flexing problem that kills so many rear-defrosters. If anyone has similiar symptoms, I'd encourage you to look inside the hinge boots before taking off door/compartment panels.

Thanks everyone for your suggestions.