I've been experimenting with the custom world gen system in order to add a "starter base" type datapack.

I decided to add the block_age processor to the template, to give some texture/weathering to the stone portions of the base (per the wiki, it applies effects to stone/brick blocks/stairs/slabs, switching to cracked and mossy variants.)

However it appears there are two bugs with this processor.

1. It apples to all stairs and slabs, not just stone/stone brick. In the attached screenshots, it has converted both copper and wood stairs/slabs to stone.
2. When transformed to a slab, It also does not take the type/half blockstates of the original into account, always producing a bottom slab, as shown in the screenshots, and with the original structure shown in the furnace and roof side images using upside down stairs that are turned into out of place bottom slabs.

I have also attached the datapack for testing, the seed I was testing with is "4722294504522178225", fly up a little and the house is generated just west of spawn.