The bug
World generation creates an isolated water block that floats in mid-air. From the height it looks like it's not a full source block, but when updating the area (e.g. by placing a torch), it spreads water from it.
It seems to be a permanent problem since I already had it when I generated a new world with that seed in previous pre-releases (and when converting a 1.12.2 world without that chunk with the same seed).
How to reproduce
Seed: -4270258239336733475
Coordinates: /execute in overworld run tp @s -188.92 64.00 -387.83 33.98 47.65
Related issues
is duplicated by
Attachments
Comments


Another (1.15.2) example: -3583102154918299393
, /execute in minecraft:overworld run tp @s -829.50 67.48 -273.08 -710.40 52.80
.

When I playing Minecraft, I goed to nether and, I, found a bunch of floating lava, I will try to get the seed and the coordinates

Can confirm in 21w14a. Seems to be a swamp-only issue.

The problem only seems to happen when caves intersect the swamp surface builder, which places 1-block deep puddles in places that would normally have ground.
I used this seed from MC-32813, which seems to have this specific issue.
6531545027671287273
/tp @s 170.45 58.00 -634.49 151.94 -50.55
[media][media][media]
I found this issue happening in a forest biome.
-3211609016775821081
/tp @s 257 65 66 50 50
[media][media]In the second picture I recreated the world with caves disabled.
You can see that there is a "flooded" lake generating there. It's not the normal lake feature, rather it's the same thing used for oceans - all air blocks below y=63 get filled with water. You can also see that the cave gets partially cut at the chunk borders.
I suspect that this bug is strongly related to MC-125033.

Can confirm in 21w18a.

Can confirm in 1.17.1.

Seem fixed in 1.18-pre4.

Actually this was fixed in 1.18 pre-release 3