Vertical slabs crash the game when placed in water (and prevent reloading world)

[nfurlow]

Issue:

As the title says, when you place a vertical slab into a block of water the game crashes and then prevents the world from reloading. However, if a vertical slab is water-logged by right-clicking on it with a water bucket, or by 2 adjacent water source blocks flowing into it, no crash occurs. Additionally, if you water-log a vertical slab in one of those ways, you can then place any other vertical slab in the same water-logged block to make a double vertical slab without a crash. The crash only occurs when you directly place a vertical slab into water.

To Replicate:

1. Install DoubleSlabs mod
2. Obtain a vertical slab block
3. Place the vertical slab into a block of water by right-clicking

Result:

Crash - Log: https://mclo.gs/HbNigyf

Expected Result:

Water-logged vertical slab should be placed

Versions Tested:

• DoubleSlabs-Forge-1.20.1-0.1.2 (on Forge v. 1.20.1-47.4.5)
• DoubleSlabs-Fabric-1.20.1-0.1.0 (w/ Fabric API v. 1.20.1-0.92.6 - on Fabric v. 1.20.1-0.17.2)
• DoubleSlabs-NeoForge-1.21.1-0.2.3 (on NeoForge v. 21.1.200)

(The bug appears to affect all versions but I am mostly interested in a fix for the Forge 1.20.1 version because that is the one I was playing haha)

[joel4848]

Identical crash here, fabric 1.21.1. The server itself doesn't crash but the client does as soon as they load the chunk with the vertical slab in water.

https://mclo.gs/Rx4GdS9