Screen problem

Hello, i received my iMac (late 2013) and everything is fine since few days but today i was working on a video during few hours (after effect), i took a break of 10 min, the video in pause on the screen, when i came back, i left after effect and the picture was like incrusted in the screen, doesn't matter where i was, on the desktop or in the finder, safari, i even restarted the mac but still there, and after 10 min, it disappeared, i try again to let a video in pause on after effect and i let it 10 min, i left after effect and the same problem, but it still disappear after, is it a real problem and i have to return it or it is normal?
Thank you for your help

ps: my config is 27", i7 3,5 ghz, GTX780m, 3To fusion Drive, 32go ram.

I fund something from apple about it
http://support.apple.com/kb/HT5455?viewlocale=en_US

They say that it's normal. Should I let it like this or return it ?