Mobs from Thaumcraft which are in the nether will have their models corrupted.

This still happens on v0.1.6 (with Thaumcraft-1.12.2-6.1.BETA26 and forge-14.23.5.2838), and to add to it, the overworld mob models also seem to corrupt once you come out of the nether.

The Embers Rekindled (EmbersRekindled-1.13-hotfix2) Ancient Golem fireball model also breaks.

Can confirm, seems to still be happening. I also tried running a snapshot of BP 0.2 and it seems to have been fixed by one of its changes (guessing 46ad6a6), so I'm probably just going to leave this issue open until 0.2 is released.