Snow layers on grass blocks don't make grass snowy unless manually placed

The bug

When grass is generated in the world with snow layers on top, it sometimes generates with "snowy:false", as shown in the screenshot. (This only happens in particular spots, like many other world generation glitches, so this might be related to older worldgen issues as well)

Snow layers appearing via weather also do not update the snowy value correctly. When placed manually by a player or a command, it correctly updates the grass block.

I think this might be a result of block state update code lost during the flattening? Not sure.