Posted for Don Skeele <dpske@wvi.com>:
Jack,
     Over simplistic perhaps, but STec Servos have a clutch which can be set in the field to slip, once the set force is exceeded.  The logic for this is that you can overcome the servo if and when necessary.  I've had a "hard up" controller command, when it was imperative to over come the servo..
     In your case, could the servos have been set up without enough friction to handle your control forces??  Easy to check, hold the effected control surface and see the amount of force on the stick to get the servo to slip.   I think there's something else going on though as well.  Tech Support at STec at (940) 328-1375 should be much more conversant with your problem, if he is still around, a guy named Butch Nemo was a lot of help to me.. Don Skeele  (503) 769 2563