Lenovo A859 touchscreen touches itself
It's probably a hardware problem and you may need a new screen. Yours may be damaged.

It might also be a battery pack that has expanded from frequent heavy usage. This can push against the screen from the inside resulting in a similar effect sometimes.

It's also possible it's a result of being flexed in a certain way such that there is extra strain on the corner. I'm speculating that the corners are often used to hold the weight of the device.