Mod Version: Byg 1.3.5
Mod Loader: Forge 36.2.0

What basically happens is that planks of wood types found in the Nether will catch fire if put inside or near lava, but only the ones that can have a flat surface on the top, namely normal plank blocks, bookshelf blocks, crafting tables, top-half slabs, upside down stairs, and closed upward trapdoors. They do not get destroyed, also, but it makes making nether wood structures near lava difficult, and it also makes sense if they are all immune to fire like the Crimson and Warped planks. Woods, logs and their stripped variants are not affected by this.

The plank types affected are Embur planks, Lament planks and Sythian planks.