Slider bar to unlock does not work until hitting home the 2nd time

When I hit the home button at bottom to make the unlock slider bar show up I am unable to get the slider bar to move.

As soon as screen goes black again and I press home button again the slider then works so I can put in my 4 digit code.

No problems until the phone has sat for a few minutes and the screen goes black again.

I have tried resetting the setup along with rebooting.

Looks like a trip to the Apple store is in order unless there is a know fix.

thanks