As of the latest Preview, it appears that the existing wooden-textured stone-like slab has been converted to the new IDs improperly.

Specifically, "minecraft:stone_block_slab" with metadata 2 becomes "minecraft:oak_slab", rather than "minecraft:petrified_oak_slab".

Expected results

Existing cases of these slabs would convert over to a new ID that retains their original properties, identically to how petrified oak slabs continue to exist in Java Edition.

Actual results

They are converted to oak slabs instead. This is detrimental for structures which used the non-flammability and other such properties of this slab to their advantage.