When lava is nearby a crimson or warped plank tile, the lava attempts to ignite the block, and puts fire around the wood. Of course, the wood doesn't set on fire directly as intended, but the lava still puts fire down around it as if it is a flammable block. This defeats the point of using these wood types over the others as they still cause fire to start around them (I was making a bridge in the nether and fire started appearing on and around it).