Unarybit

Can confirm for 1.21.5-rc1

I can also confirm scenario #2 for 1.21.4-pre1.
It is exactly as described by sicarious.
See uploaded video "Resin Clump Bug" to reproduce the bug.

Still in 1.18.2 and 1.19.

I couldn't replicate it in 1.16.5.

If I summone a wither in solid blocks, it doesen't move and die.
Other mobs with suffocation damage could also not go into neighboring blocks.

Could it be that you have a modded version of Minecraft?
Keep in mind that things like OptiFine and Forge are also "mods" that can change behavior.

I don't think that this is a duplicate of MC-225551.

What he describes seems to be part of a cave spider farm, where he uses a piston with a block to soften the cave spider (see screenshot). 
The cave spider also "glitch out" when they are in a transparent block, without suffocation damage.
But I would say that this is WAI, because the cave spider can walk with the block when the piston retracts and then climb up into the air block.

I think this should be reopened as this is a bug and not a feature request.
In previous versions you could put redstone dust on leaves, for example in 1.14.4 as you can see in the pictures of MC-163886. 

That can be very usefull, since leaf blocks do not transmit a redstone signal, do not stick to slime blocks, but redstone dust can be placed on them. 
This behavior was unique before 1.17 Snapshot 21w05a, where moss blocks have the same behavior.
Well I hope it stays that way with the moss blocks 🙂

Edit: It seems like that 1.14.4 is the only full version where you can put redstone dust on leave blocks.

Can't reproduce it in 1.16-pre5

This also applies to mobs.
And players and mobs suffocate even when they are at the edge of a water bubble column.

Tested in 20w22a, 1.16-pre1 and 1.16-pre2

Can confirm this, the farmer only harvest if he has something to plant in his inventory.

Soul sand is not a full block, so it doesn't work.
To place scaffolding blocks down, they need a completely smooth surface at the height of a full block. For example, you can place them not only on full blocks, but also on upside down slabs and upside down trap doors.
Couldron, Hopper and Composter do not work either, although the scaffolding blocks would stand perfectly on the "edge" of these blocks.

For me it works correctly in 1.14.4 Pre-Release 5, see screenshot.

Can you show a screenshot with the beds? I think that would be helpful.

I see now what you mean, that is related to the bug fix MC-146289.
The farmer search for crops / seeds on the ground. If he can not pick them up because in his inventory already are 4 stacks of it, he gets into a loop.

As a solution I would suggest not to let the farmer search for crops, but to let him go to the farmland he just harvested / planted and to let him wait there (1 second?), so he can pick up the crops / seeds.
The "slowed down" farmer would also make the farm-work look nicer.

The "new" villagers can only have up to 4 stacks of the same item in their inventory.
I think it was MC-74407 that changed it.

I can confirm that.
This bug is very bad for the tech community, it affects automatic wheat / beetroot farms and villager breeder.

If I test sharing now, it works as it should. So the farmer starts sharing when he has 6 Bread or 16 of the other food. I know that the villager only share during the day, so it's not that.

I also can not reproduce that they no longer share the food.

The farmer also stops harvesting when he has 60 food items in his inventory. So the farmer probably will never share food with his villagers, which prevents the breeding of new babies.

Note: sharing food is broken anyway. Even if a farmer's inventory is full of food, he does not share it.

Tested in Minecraft 1.14 Pre-Release 5

To be clear, I just want to know what behavior is now "Works As Intended". Can mobs see if their head is in a transparent block or not? If not then the "WAI" classification is incorrect for MC-122988 .

Can a mod confirm this bug report, so that we have a chance to get a statement from the devs?

Hi violine1101 🙂

I do not think MC-133687 is a duplicate of this bug here, please take a look at my post there.
But you are right, even non-hostile mobs with their heads in transparent blocks, do not attack hostile mobs.

I also think that this bug here is not a duplicate of MC-133344.

Their heads are not in the blocks, it is probably irritating that the collision box of a baby chicken is very small and does not match the rendered one.
This bug here is more of a pathfinding problem because a baby chicken takes the collision box of an adult chicken for pathfinding, as demonstrated in this video:

https://www.youtube.com/watch?v=j61ffITyUwc

I also uploaded the world for testing.