When Sona has 3 stacks of Power Chord, she sometimes cancels all actions and attacks a nearby enemy

First I will point out that I have auto-attack turned off in the options menu. I have noticed a few scenarios where this has happened, but it seems to only happen towards enemy minions.

I will be holding down RMB so Sona follows the cursor, an enemy comes into range and she stops moving and attacks the enemy.
It doesn't matter if the enemy is behind you or in front of you, she will turn to face them to perform the attack.
This ONLY happens when I have 3 stacks of Power Chord, and she will only attack the enemy once, then she will start following the cursor again.
Its very infuriating when I am running away from the enemy and this happens, I have died many times because of this.

I have also seen this happen once while I was recalling from inside a bush, the enemy did not have vision of me and I was not under attack.
However, the recall was not cancelled which I thought was very strange.
I tried recalling when I have 3 stacks of Power Chord, and issuing a command to attack a nearby enemy minion and it cancelled my recall this way.

As I understand, when you have 3 stacks of Power Chord, your auto attack is meant to be disabled towards enemy minions.
I thought that maybe there is a bug in the code, where instead of disabling your auto attack, it toggles its status.
So I tried playing a few games with auto attack enabled, and it still happens to me.