Full faces of non-full blocks(with the exception of slabs themselves) are transparent when next to a slab.
{F3995}
Non-full faces of non-full blocks are not transparent when next to a slab:
{F4002}
Glitched faces(swapped u-v-vertices) on heptas are not affected:
{F4004}The partial faces of slabs next to transparent slabs, that are equally high or higher, are not rendered.
If the orientation of the slabs is not the same, the face is rendered, which is intended.