iPod Touch 5th gen -Unresponsive screen when charging

Just noticed the screen is unresponsive when I'm charging,

it acts awkwardly while Im trying to open apps,

i cant use it normally when its lying on the table, something like that.

It somehow resolves my problem when i took it out from its casing but i should have to hold it properly like my left hand at its back and fingers on its front . I can't use it properly without doing that.

I've reset all the contents & settings. Just got it last January 10 2013 😟

BTW, my iOs is up to date (even when i still haven't updating it),

tried the pressing the sleep/wake button & home button at the same time before resetting it.

....and still the same.

PLEASE, ANY GOOD ADVICE, what's the problem?