Searched. Nothing exactly matches it.
If a certain block somehow finds its way into a position it should not realistically be in, such as on air, water, above a torch, etc., the block will continue to insist that it is in a valid position and will not break even if given a block update.
Blocks affected:
Torches and wall torches
Signs and wall signs
Heads and wall heads
Buttons
Levers
Pressure plates
Doors
Beds
Banners
Tripwire hooks
Ladders
Rails, redstone dust, repeaters and comparators will pop off instantly when updated as one would expect.
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migrated
muzikbike
in that case, why do repeaters and comparators pop off?
migrated
That'd be a bug.
migrated
Not really, because part of the comarator or repeater would be in contact with the block that updates them. It would only be a bug if they broke when a block was placed above them, where they make no contact. In the case of torches, buttons, levers, etc., they only make contact with the supporting block and nothing else, unlike repeaters, comparators, etc. which make contact with blocks to the sides as well as below them.
muzikbike
The thing is, this bug doesn't occur in 1.12.2. You can't even setblock a torch in midair without it just popping off instantly.
Blocks that need support, only check if they are in a valid location if the block the support is supposed to be changes.