PrimedTnt do not break blocks/does less damage when in half slab.
EDIT: Sometimes does not break any other block except the half slab itself, some blocks on top of the slab will be destroyed, see picture.
It works with any other half slabs except wooden ones.(see pic 7 & 8)
Explosion is normal if PrimedTnt is on top of double-slab, or upward-facing slab.
Blocks will be damaged if the PrimedTnt is outside the half-slab (see second last picture)
WORKS WITH ENDERCRYSTAL TOO