Despite creating snowy grass blocks below them when placed on grass by the player, snowy grass is not generated below powder snow in the new mountain biomes (snowy grass on the left was placed by me). As a side note I would love to see regular snow blocks have snowy grass below them as well. 

Example:

seed:-8458411592164212928

10769 141 -2366

Additionally when the same seed is used in 21w39a at -800 140 -400 there are several powder snow blocks on top of regular grass blocks (I couldn't find an example in 21w40a). 

Expected Result

Powder snow would generate with snowy grass underneath it