Guild Wars 2

I’ve read the wiki and I understand the concept, but sometimes I notice a boss DOES have stacks of Defiant yet CCs works on him. I’ve just ran informal tests with a Flesh Golem’s charge and the boss absolutely gets knocked down with 2+ stacks of defiance, but other times completely ignores it

I also notice during HOTW’s aquatic bosses where water control skills seem to work on them fine when they have defiance stacks up

Is it buggy or is there something I don’t understand about the mechanic?

I’ve also seen some inconsistencies here and there.