You can press grass with a shovel, but not dirt

The changelog for the 0.11.0 Beta (and consequently, the Minecraft Wiki) refers it as 'grass path', while the block's texture appears to represent trampled grass. In addition to this, the original suggestion from which this was implemented utilized grass blocks:

...use the grass block, but instead of rightclicking with a hoe to make farm, you rightclick with the shovel to make a road.

I am guessing that this is Working As Intended, though I will allow a developer to comment here first before resolving the ticket.

Based on my understanding from the G+ community, this works as intended. Packed Dirt or Path is made from grass blocks and cannot be made from dirt blocks.