Is this a bug or just pre-asset placement? Regardless, it makes it really difficult to determine which item is which, as every icon is like a bag of grain. 

Yeah they haven't done the icons for the majority of items. That said more is being added with each patch.

Lots of items are missing unique item art as well. Currently all necklaces/amulets are cloaks, and plenty of hats are helmets etc.

I hope they will soon patch the icons in the game. Difficult to find out what you looted without proper icons. ) And no, I don't want a list view, I like the inventory grid very much.