Stone To Wood Bug?

I am in my creative world specific to making Mini-Games,
testing some railroad tricks, when I start setting a floor of stone slabs.

What I decide to do is put down a different type of slab, Quartz, but what I notice when I place them over is...

The stone slabs turn to wooden slabs!

Steps to Reproduce:
1. As said above, place down some stone slabs so they take up the bottom half of a block
2. then place quartz slabs on top of those!
3. have fun with your newly made wooden slabs :'P