Unhappy HELP With My Code. Lua (Corona SDK)

code.tutsplus.com/tutorials/corona-sdk-create-a-memory-match-game--mobile-7271

I used it on the Storyboard Api, my problem is that when I press my HOME button the tile didn't disapear yet it just overlayed by the scene that i called.

can you help me? Im stuck at this problem

here's the result and also the code

pastebin.com/aMGm3zdG
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