Motors spin up when autopilot loses power or reboots

Hi guys,
I’m running Copter 4.0 on a new PixHawk Blue Cube H7 on my hexacopter. I’ve noticed a strange/unexpected behavior. With my vehicle powered up, If the pixhawk loses power, the PWM signal to the ESCs goes high, and the motors all spin up to full rpms for a few seconds before they then shut off. Fortunately, all the propellers were off of the motors when this was discovered, but you can understand why this would be dangerous if all the props were on. (I’m spinning 22-inch props!)

I’m wondering if there’s a way to configure my system so as to stop this behavior.
(I understand that there are ways to supply backup power to the PixHawk, but for reasons too long to elaborate, that’s not really an option for me.)

I’ve had another autopilot on this vehicle and it would unexpectedly reboot. When that happened, I got the same behavior–the motors would suddenly spin up to full rpms for a few seconds before shutting off.

Please update from Copter-4.0.0 to Copter 4.0.6-rc1 and after doing that update the bootloader FW, just in case.