Whether or not this would be classed as a bug I'm not sure, but I have noticed that while PC/Console have Grass Paths in their creative inventories, Pocket does not have it. Also, it doesn't seem fair that the Stonecutter (although useless) is in the creative inventory while the Nether Reactor Core + Glowing Obsidian is not in it.
MCPE-17419
Grass Paths, Nether Reactor core, and Glowing Obsidian aren't in the creative inventory.
Resolved
Works As Intended
0
(Unassigned)
Unconfirmed
Phone - Android - Samsung Galaxy Note
Android 6.0.1
0.15.90.8
Retrieved
According to the Minecraft Wiki, those blocks are only obtainable by using 3rd party apps, or with some tools.
http://minecraft.gamepedia.com/Pocket_Edition_data_values