It also seems to be related to a "Round Trip Different" issue (F3+point one of these blocks). All A/E differences are different on each kind of slab
I haven't tested this version, but the Bug appeared to me two more times : One time near of a Spider spawner, and one last time near of a lot of Zombies. I'm still trying to understand this bug...
It also seems to be related to a "Round Trip Different" issue (F3+point one of these blocks). All A/E differences are different on each kind of slab