When digging a snow layer with a ground based block underneath (ground based blocks are blocks which can be removed with shovels effectively), if you dig up the snow, and then the ground based block with no click interval (on the same click), the ground based block will be dug just as fast as the snow.
This seems to affect all versions of the game.
Is this still an issue in the most recent versions (currently that is 1.10.2, or 16w43a) of Minecraft? If so, please update the affected versions and help us keeping this ticket updated from time to time. If you are the owner/reporter of this ticket, you can modify the affected version(s) yourself.