The bug

Sculk can spread outside of the world border. This can occur when an entity dies nearby a sculk catalyst, spreading sculk blocks nearby. When this is done by the world border, some of these sculk blocks can generate past the border.

How to reproduce

1. Run the command:

   /tp @s 29999980 -60 0

2. Place a sculk catalyst right next to the border
3. Spawn a cow, and kill it
   Some sculk blocks may spread past the world border

Expected results

The sculk blocks would not spread past the world border; instead, they would stop spreading before crossing the border.