Water does not leak through leaves and regular stairs but upside down stairs

Water (still or flowing) does not drip through leaf blocks, even though rain does.

Water also seems not to penetrate certain other blocks that it should. These are all transparent variants as far as I can tell. Stairs - stop leaks, upside down stairs - leak; upper slabs - leak, lower slabs - don't leak; ice - doesn't leak; and even water itself, if you have a free-floating water block, it doesn't so much as dribble.

See also MC-8858