Why my plasma now show retention of 4:3 bar?

[mugupo]

My parent use the tv mostly watch sd cable content which is mostly 4:3 screen ratio, problem is now it left out a small image retention of 4:3 square bar when i view widescreen content. I don't notice much but is there. Anyone has this similar problem? Should I contact Samsung regard this? If not a problem i rather wait so if not fixable i get replace with newer model.