Two problems that I'd like to bring up.

1) As most people who have played this patch have noticed by now, there's a shortage of normal ammo with the change to the vendors (unless you camp them and buyout every day or two) which didn't used to be the case as you could just buy as much ammo as you want and the HP/AP was only from drops. This change more or less forces you to use the other variations of ammo, which isn't a really a bad thing but the problem with this is that only HP ammo is really more useful than normal ammo and really only in the beginning of the game as it falls off quite fast as you face mostly armored enemies. Which leads me to the next problem...

2) AP ammo is, as far as I can tell, completely useless compared to normal ammo? It doesn't do more dmg on armored targets? Is this intentional or just a bug? 

HP ammo should have dmg absorbed a lot by armor so that's where AP is useful. If HP does dmg against heavy armor it means it's a bug somewhere. It is not supposed to do MORE dmg, it's supposed to penetrate armor, where normal and HP shouldn't.

I confirm HP ammo used against unprotected areas (head) have heavy impact ;-)