Care to elaborate? The game had an issue where they never despawned, but that was fixed in like 1.3 or something way back then. (So it never occured afterwards) Or do you mean the actual models of them or something?
Maybe for default followers it works fine but for mod based followers it doesn't.
That doesn't really make sense... I'm pretty sure the 'cleaning up arrows/ice chunks' system is handled entirely seperately from whos follower is what and from what mod or not.