As people already said, the real question is : Can hunters & wlocks (it happens a lot of with felhunters too) put their pet as "invalid targets" on purpose ?
Do they realize when their pet becomes bugged ?
Can they get rid of it and make their pet "valid target" again by dismissing/recalling or re-summoning ?
Not gonna ask for an ETA concerning a fix since this is probably in the odds of casts & blinds finishing through stuns, ppl kicked from the game after getting Mind Controlled and paladins getting CCed under bubble, the above mentioned AB flags which can't be clicked/capped, etc. AKA it's not getting fixed anytime soon for legit reasons but instead bans happen apparently.
So these bugs are reported since months and they are considered bug abusing. Will casters, rogues, etc. getting casts & blinds through stuns get banned as well ? How would you make the difference between the player who did it on purpose and the player who got a cast through a stun by pure timing luck for instance ?
Is a screenshot of an "invalid target" red message when trying to attack a pet sufficient proof for GMs to toss a warning/ban ?
Maybe you should make sure the community knows that this bug can lead to a ban. Because it doesn't seem like half the hunters & wlocks even realize when their pets are bugged. And not everyone reads forum threads which aren't related to Announcements/Rules, nor have access to the Bug Tracker (compare tracker accounts with game accounts for instance).
I can't imagine you can decide to ban people for a bug they have no control whatsoever on.