This glitch that lets you pulv before the target is knocked away from headbutt is probably the most globally known bug in the game, and yet it hasn't been fixed. While people are probably going to automatically complain about such a suggestion to fix it, because everyone's grown accustomed to it, it really shouldn't be ignored just for that reason...
It's because of this bug that he can't be buffed otherwise, and it really isn't fair to be honest, to expect an Alistar player to do this bug. It's unreliable even for pros, it's unrealistic to expect absolutely everyone to even know about it, and it's unfair to blame Alistars for not doing it, or failing their attempt at mimicking it.
It isn't referenced in his tooltips, it isn't a part of his intended design, and it's holding him back as a champ in general, because, oh hey, headbut pulv too stronk, we can't buff this guy.
Seriously, Panths W being able to land guaranteed after an ult got fixed, and while he hasn't been buffed in compensation yet... (wtf Riot, get on this) Alistar should be no different with his well known glitch.
What's next? Is Rengars double leap going to be ignored once everyone learns to master it, just because Rengar players like to abuse it? What about this TF gold card trick that I'm sure not that many people know about yet...
Just fix the bug on Alistar, and then give him compensation buffs. It's the logical thing to do, and it should have been done long ago.
inb4 "Looks like someone failed the combo" XP