coal generating bellow Y=0 is still in stone

in 21w08b , it is still possible for the generation to create coal ore bellow Y=0 when a fossil is generated

Either fossil should only generate above Y=0 or the coal ore generated as part of fossil bellow Y=0 should be in Deepslate variants

In the attached screenshot, I found a fossil at Y=-17, there is no stone arround, only deepslate. But the coal ore is using stone.