I have come a little further with my research and experimental work;
The fellhunter "Spell Lock" bugs out if you try to use it while the pet has 0 energy, that means it will not work AT ALL if you press "Spell Lock" ONCE when it haD 0 energy and you try to spam it and get it out when it WOULD have 20 or 40 energy. It takes the fellhunter about 2seconds to regenerate 20energy. I am not even sure if THAT is retail-like that it goes to 0 but that's a different story.
I can't make the gif longer so you can see that it does not trigger at all after. *
I never ever in my LIFE had issues to get a Spell Lock off on retail that's why I am a little upset about this.