Minecraft version: 1.20.1, Forge

When using a chisel on slabs, the slabs convert into blocks, essentially duplicating in number.

To replicate my exact scenario:

1. Place cobblestone slabs on the ground
2. Have a cobblestone variant in the chisel
3. Use the chisel on the slab by left-clicking

The slabs will convert into blocks of the cobblestone variant present in the chisel.

Consequences: While time consuming and inefficient, a player can exploit this bug to duplicate the number of slabs, essentially making an infinite number of cobblestone blocks starting with only 3 slabs.