If you middle click a fully build double slab (two slabs placed on top of each other), you will get an item of the full block called the slab name, however when you place it, it will appear as a regular double stone slab. Even though below I said with the exception of the wooden slabs, they still have a glitch, except they inherit the default wood color even if it is a Spruce, Birtch

Steps to reproduce

1. Go into creative mode and grab a slab (with the exception of stone, or wood ones), such as stone brick, brick.
2. Place two slabs on top of each other.
3. Middle click the double slab you placed.
4. Place the new block in your inventory on the ground.