Samsung PS-50C96HD image renention

[mzone]

hi guys i have a Samsung PS-50C96HD.

set powers on with picture however i have noticed the tv suffers from a sort of  image retention

what i mean is if say you bring  the menu up  on the screen and you turn off the menu you can still see like a faint  square box in background and theres red/green sparkles where the image of the menu was, it seems to dissapear after say 5 seconds but know this is not normal.

anyone any ideas?