The bug
Unlike snow blocks, snow layers do not drop themselves when harvested with a silk touch shovel, instead dropping snowballs as usual (too many snowballs: see MC-61821).
How to reproduce
Obtain a shovel of any type enchanted with silk touch and break a snow layer of any height. Snowballs will be dropped instead of layers as expected.
Comments 3
This was resolved before the patch that allowed snow layers to be obtained in survival (via crafting). Perhaps it should be reopened?
This works as intended. Only snow blocks will drop snow blocks. Fallen snow will drop snowballs.