The bug
When an animal walks in water which is only a half block deep, they can't seem to move and spin in place.
This bug also happen to some hostile mobs that can float on the water, like creepers, spiders, silverfishes, illagers
How to reproduce
Spawn some pigs, using wooden half blocks, with the top half filled with water. The pigs move into the water, get "stuck" and instead of moving, will just spin in place. They can sometimes move a very small big/slowly, but mostly just spin in place.
Linked issues
is duplicated by 56
MC-137361
Passive mob spin/get stuck in seagrass
Resolved
MC-139213
Illager in the pillage group spins around when in tall seagrass
Resolved
MC-139281
Pillagers and vindicators can't find their way out of top of kelp blocks or surface sea grass
Resolved
MC-139308
Pillagers become stuck on sea grass.
Resolved
MC-144181
Seagrass makes creeper spin
Resolved
relates to 2
Attachments
Comments 22
Still in 18w46a - I have two Illagers in some water nearby who have been spinning on seagrass for many in-game days now. Normal game, no mods, cheats enabled but no cheats in use. I'd feel sorry for them if they weren't so shooty...
I confirm this bug too in 1.13.2, It's not just animals but mobs too. Any walking entity. The problem only happens when the entity starts its path on a water-logged block (seagrass, kelp near the surface, etc....)
It also happened to some hostile mobs like silverfish, endermite and vindicator in 18w50a, seagrass and coral can also stuck these mobs
I've found that this bug also occurs when mobs try to walk on halfslabs that directly at water level (the lower 'half' of the block is filled with water while the top is slab). Really sucks for my slab-based raft village. I'm not sure if it's related, but creepers that blow up on these blocks also don't destroy any blocks, as if they were in the water (but they are not).
Bug seems mostly fixed. However, in 1.14.4 pre release 2, mobs still experience the spinning if they walk on the top half of a waterlogged slab (top of block is slab, bottom is water).
[media]Since both the behaviour and the code changed, I recommend creating a new ticket and linking it here (so that it gets marked as related).
Made a separate ticket for the bug pertaining to the top halves of slabs (thanks Fabian) : https://bugs.mojang.com/browse/MC-156022
migrated
Confirmed for 1.13.2-pre1.