There is a bug with wood slab. I put it and it's in the air
wierd half slabs
Red box glitch
Wooden slabs have a red background in survival, and are labeled "stone slabs". Requires a pick to get back.
Mining a upside placed slab gives you the up placing slab with red background.
Wooden and Stone Slabs Turning red in your inventory when breaken
Red box in place of/behind stone slab icon