Some Betweenlands slabs cannot be removed. When broken in survival, they drop the block then instantly reappear. When broken in creative, they just instantly reappear. All other Betweenlands slabs break appropriately.

This only occurs when KleeSlabs is installed alongside The Betweenlands.

thebetweenlands:cragrock_slab
thebetweenlands:pitstone_slab
thebetweenlands:betweenstone_slab
thebetweenlands:smooth_pitstone_slab
thebetweenlands:tar_solid_slab
thebetweenlands:temple_brick_slab

Forge 2669
KleeSlabs_1.12.2-5.4.8
TheBetweenlands-3.3.7-universal