To reliably reproduce that issue just make sure the last item you place in the cube is placed in the top left slot. Its just a small graphical issue though and does fix itself as soon as you unequip the item from the cube.
Hey there, thank you so much for reporting this issue! As Kad already mentioned this is a known bug. The good news is, that it is already fixed in the next release :-) Expect it to come end of this week on Android!!