Not much to say here. F3 confirms that this block is indeed a double cobblestone slab block. Regular slabs are unaffected.
I was going to report this, but I then saw this issue and multiple related issues. Go figure. I will post a screenshot anyways.
Proof that this bug is still present in 14w10b. Also notice the messed up inventory texture.
Also, this is for Sandstone, not regular stone.
No. I am in B and this bug is still present.
Exactly. Thank God I backed up my world.