In 1.12, you can make an inclined rail by making a rail go into a block with another rail on top. If you powered the inclined rail, you could delete the normal rail on the top of the other block, and the inclined rail would not go flat again. In these snapshots, though, it is not like that. If you power it, it makes no difference in keeping it inclined. This means that you cannot have an inclined rail going into a wall. There must be a bit going in to have the top of block rail to keep it in place. This wrecks a bunch of redstone contraptions, and since you did not completely wreck it with the new water physics, i'm guessing that you don't want to wreck it, at least in this way. If this is a bug, please fix it