Examine the attached Screen capture from my Ipad Air.

You can see in the hotbar that there is a stack of 64 wooden planks on the far left. However, that stack is NOT visible in the expanded inventory. As far as I know, the toolbar is not "extra" inventory spots, but merely quick access to the 36 available inventory slots. This has been happening that items are occasionally in the toolbar that are not otherwise accessible in the inventory, transfer, or crafting screens.