Am happy to report that I think we've solved the hard brake problem in our new Honda Fit, and Roadmaster's main installation tech at the factory (Graham) was very helpful.
I'd sent an email to Roadmaster asking about this problem, and they called me and asked me to bring it in for a complimentary check (even though we had not had it installed there).
When I went to Roadmaster, found that the relatively early Invisibrake units had had a problem where one of the tubes installed in the box was so short that it tended to create a leak. He showed me where the tube was barely attached (it turns out that we got one of the early units installed based on the serial number; the later units have fixed the problem). He took the unit apart and fixed the tube and reinstalled the unit. He also checked all the wiring and found that the Invisibrake had been installed too tightly (brakes were dragging a bit). Fixed that too. Then sent me on my way, and extensive testing so far has been unable to recreate the hard brake problem.
Must say that RoadMaster was extremely responsive and helpful with this problem.
Mark