Models aren't being rendered on the "shift view" for pattern items.
TESR related?

Mod version: 1.2.3
Minecraft version: 1.10.2
Forge version: 12.18.2.2122

It seems like this happens with TESRs, the current code in BakedModelPattern only supports models.

Given that the vanilla chest or a skull is a TESR we might want to look for fix.

TileEntityItemStackRenderer seems to be the issue here. Will have to discuss with fry when he gets back.

I've obviously been seeing this for some time as well. How "long term" is this expected to be?

No idea, I think this is a Forge bug, or something in Forge that at least stops us of fixing this.

It is something in mc, which isn't patched to make sense by forge.