My test is as follows:
1. Set the heli down on a concrete slab in my backyard
2. Turn on radio, turn on heli (gyro initializes as normal in HH mode)
3. Start heli (gyro light still solid in HH mode)
4. Apply 5% (25% total travel since I start at 20% throw for idle) throttle
5. Gyro light double-blinks. Any movement, or no movement, to throttle (left stick) and light blinks.
6. Only way to stop light from blinking is to return throttle to 0% (20% throw)
Without touching the radio, light blinks everywhere but 0% throttle.
Heli rotates right constantly when above 0% throttle (obviously since 0% means clutch disengages and rotors eventually stop) even when no input at all is given.
Tail does not drift/move in normal mode. It operates fine.
I do not touch the heli after turning on power, not to mention starting.
No trim is set.
No gain setting makes a difference.
The only revo mix is in normal mode which works fine. It's only HH mode that there is a problem.
HeliProz indicated that servo test mode on a HH gyro is inconsistent so I am not paying any attention to it.

Any other ideas?