GravityTester,

I'm not sure what you mean by "kill the power". I'll assume you mean a rapid movement of the
throttle stick to the full down position.

And as you didn't mention otherwise, I'll assume your heli flies normally.

There is only one thing that can provide a force to yaw the heli to the starboard, or clockwise -
that is the tail motor.

So what is happening is - you chop the power but the tail motor does not reduce the force that was
necessary to keep the nose straight against the port or counterclockwise yaw force from the main rotors.

The nose turns clockwise due to the force from the tail rotor.

If you are using the stock 3 in 1 board, I can think of a couple "maybe" causes. One the tail motor esc circuit is defective. Two the gyro gain is set too high. And last, the left right bias adjustment is set to extreme right tail bias.

The Axe manual says: Left/Right Bias – Is used to obtain a balanced feel between
left and right tail rotor inputs. The adjustment is very
sensitive so only make small changes. Turn clockwise to
increase the left tail rotor bias.

I've never really understood what the "bias" is, but turning the potentiometer can make the tail motor start turning.

Here are some things to try:

Reduce the power very slowly and be sure you are not putting in any right rudder, does the problem still occur?

Reduce the power enough so the heli is not light on the skids, then put in full left rudder and kill the power.

Turn the bias adjustment on the 3 in 1 maybe 1/8 turn clockwise and see what happens. If the problem is worse, turn it 1/4 turns counterclockwise.

Turn the gyro gain all the way down and then up maybe 1/8 of a turn.

I'd like to know what you find out.

Good luck!