How to reproduce:

1. Run command "/gamerule mobGriefing false"
2. Place Powder Snow
3. Obtain a Bow enchanted with Flame
4. Shoot the Powder Snow with the Bow

Expected result: the snow is broken.

Observed behavior: the snow is not broken, and the arrow passes right through.

I feel that this is unintentional because Player-shot arrows aren't created by mobs, and thus should not be affected by the game rule.