I used some torches to lit up my guardian farm and one time I visited there all the blocks above the torches in one corner of the farm were dark and mobs were spawning next to a torches but just one block higher. I planted new torches at the dark places and removed them right away and the light levels were fixed, but I think I experienced this same bug.
Just checked my Blaze farm and can confirm that this is still issue in 1.14.1
I also have this problem, but I'm playing on PC. I tried to make a flower farm by dispensing some bone meal to a grass platform from below, but doing this crashes the game most of the time.
I've been trying hard to fix my kelp farm, but it seems to be impossible at the moment. I have noticed that the kelp is able to grow a certain amount (aging system implemented?) and when I use pistons to cut the kelp that amount changes. In the end the kelp is not able to grow anymore and needs to be replanted for the farm to work again. Also bone meal only works for the kelp to help it grow to the predefined length and after that bone meal wont work. So even bone meal can't help to make the farm work again. Basically problem ain't the slow growth but the fact that at some point the kelp just stops growing if you keep cutting it.
Hostile mobs also spawn on other blocks they shouldn't spawn on. My base got very dangerous after hostile mobs started spawning on leaf blocks and glass.
Smelted and silk touch mined stone blocks do not stack together. At least the smelted ones cannot be traded with stonemasons.
I noticed the same thing, but raising the roof one block up fixed the problem for me. I think the cause of this is that sometimes when you load villagers while they are on their beds the game thinks they are standing on the bed and they start suffocating because their head would be inside the roof even though they lie on their beds.
I think the reason for villagers dying is that the bed is in a two blocks tall space and there is a full blocks over the bed. If I replace the full block with a slab the villagers won't die.
Happened to me also. I'm playing on Switch and the world was created in 1.7.0
Eyeth, I tested what you said and I didn't get kelp to grow every time I placed water source over them. Plants that were not affected by placing water source never grew again until replanted. But I also noticed that many times placing water source did help them grow. Also the problem is not only with pistons making water block so that kelp will not grow like Auldrick said because you can also break kelp manually and it will sometimes stop growing. I don't have anything to check the age of the plant so can't really tell if it should still grow.