Microblock chiseling on wood type blocks changes the material to stone, and changes the tool for breaking them from an axe to a pickaxe. I've tested this on birch logs, slabs, stairs, and planks, as well as aged wood planks, stairs, and slabs. I assume it's the same for all other wood types, though I haven't tested them. Not sure whether this is something unavoidable with the chiseling programming, but I found it rather annoying in my survival world, hope this helps if it was unknown.
Playing version 1.14.5