anyone experience screen isn't responsive at lock-screen?

happen to me today when im tring to swipe to unlock. instead of unlocking the phone, the lcd go crazy by inverting its colour, and hang the system for like 5-10 minute then crash,

the phone stil working normally tho after the booting up. but should i be worried? phone still under warranty, should i ask for replacement or something?

oh yeah, i read bout this black dot found when going to dark place while using the camera. i have this issue too. figure its a dead pixel?? or the amoled problem? i notice that, it will show when the display is trying to make black or grey pixel. its visible at stock music app for my phone. - not my main concern, as from what i read from this forum, its known for n9.