I've seen it happen so many times I can't count - people killing the new hunter challenge rare pets as they're being tamed and I've ticketed many times.
I finally got a GM and s/he said that while s/he thought it was very wrong, there is nothing in the rule book about it being wrong and that I should go post to the forums, that if enough people lend their voices that it a change could happen.
So, I found a thread on the forum about this topic and I would encourage you to take a few moments and post. If you think it's wrong, please go take a stand against griefing of this nature.
http://us.battle.net/wow/en/forum/topic/2926886053 Thanks in advance.