Currently powder snow uses cullface to remove both internal and external faces as to form a continuous mass with adjacent powder snow blocks. This hardcoded behaviour, while fully functional for this purpose, does not account for culling of external faces by non-powder snow blocks, resulting in these faces always being rendered if adjacent to any non-powder snow block even if otherwise completely impossible to see normally.

I suggest that sodium also culls the external faces (although not the internal faces) as if powder snow was any other block, in situations where other blocks with cullface would have the faces culled. (Basically do the same as water and lava, with the distinction that powder snow shouldn't cull its internal faces against blocks, even though water and lava do.)

Seems fixed now, although the culling is a bit excessive - I'm not sure if that's fixable (dedicated ticket upcoming).

Reported in #1163.