squids spawn in lava

if you put lava flowing down wards in an open space you can see squids spawning and falling
Please change the "How to reproduce" to this:

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How to reproduce

1. Create a "Redstone Ready" superflat world
2. Go away from spawn (maybe about 1000 blocks)
3. Set /gamerule doDaylightCycle false to prevent monsters from spawning
4. Use the following commands

   /fill ~ ~-12 ~ ~50 ~-13 ~50 structure_void
   

   /fill ~ ~-1 ~ ~50 ~-11 ~50 lava
   

5. Go below the lava
   → Squids will spawn and fall down

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From MC-62856:
Steps to reproduce
1.Create superflat world
2. /fill ~50 ~-2 ~50 Lava
3.Go down 3 blocks
4./fill ~50 ~-2 ~50 Piston_Extension
5. Watch
_{Mod edit}

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Code analysis by Marcono1234 in this comment