Sometimes when my screen is unlocked (not by buttons but by being called, or an alarm going off) it's not 'active'. It turns on, but I can't use the touchscreen for entering my pattern, answering a call or turning off my alarm. When I lock the phone using the lock button and unlock it again, everything is fine again. First I thought maybe it was caused by a screen on/off app, but after emailing the developer, who didn't have an answer, and then disabling the app, the problem persisted. Is this a problem other users have experienced or does anyone know an app that might be causing this?

I have a non rooted S4 GT-I9505 with android 4.3.