i was only about to test out whats was new in 18w49A and then i decided to play with some slabs and redstone.
Then i noticed that if a slab is on like Y:70 and another slab is on Y:69 both has redstone who's connected to each other but the on at Y:69 does not get powered when the Y:70 gets power.
UPDATE
seems like the redstone with slabs works in one way, but ain't the other way around.
I hope you get some help