Stone can generate in the Nether

The Bug

I was traversing the nether in a world I had previously played on 1.17. After moving it to 21w41a, I noticed normal stone blocks in the nether, and these were new chunks that had just generated. 

Reproduce

• Go to the Nether
• Travel around in the Nether looking at gravel patches
  Notice in some of the gravel patches became stone

Expected Result

Stone wouldn't generate in the nether from updating gravel