They can't unless they stop the ability to get heavy ammo drops altogether... it's a basic mechaninc that gives you the heavy drop...

People said that they wouldn't be able to stop the Crota kneeling forever glitch because it was a networking issue, not an in game bug, but they still did. So I'm pretty sure they could get rid of guaranteed heavy ammo from every single kill if you have next to no ammo left.

that's how all ammo drops work. When that systems in place recognize that you have no ammo for that specific type then it increases the drop chances... when you have no primary ammo then it increases all ammo drop chances to keep you in the fight... half of the problem is in the label of it, as it's not a glitch but rather an exploit at best. The game was designed to do this, just maybe not this well... the on possible fix I could see was if they completely overhaul the ammo drop system currently in place... and I don't see that happening... and by them "fixing" the networking glitch, they in turn made more. So it wasn't really a fix.