iphone 5s unlock problem

Hi.

I have a problem with my iphone 5s 16gb ios 8.2.Some times when i try to unlock my phone with "slide to unlock" it dos not ulock unless i turn off and then on the screen with the power booton. Some time it is fine and it unlocks without a problem but if the above problem happens and i ulock the phon fast it ulocks but then i can't navigate throw the home screen insted it looks like it preeses the screen it some spots it's self and whont let me do anything anless i lock it and unlock it again...