Screen burn issue with dark background?

Hi,

I have noticed that if I have a very dark picture on the screen I can see some screen artifact. Looks like screen burn in to me. With white or colour background I can't notice it. Only with solid black or grey background. What might be the cause?

I did buy it yesterday and there was some corrosion on the screen connector so I cleaned it but the issue still remains the same. I'm thinking it might be the screen itself but I would welcome any other opinion.