Hey rolia, I have the same problems. Purchased a used Macbook Pro Retina 15inch mid 2012 model from a guy as my old 2008 macbook 13inch had met its end, and after wiping it and reinstalling El Capitan, I found that I am experiencing the same graphical glitch when the computer opens from sleep. I'd like to take the macbook in for repair but I am worried Apple will say its been mishandled (the gent who owned it before me didn't take the best care of it, some body scratches and have noticed a dead couple dead pixels I think are a result of life use). Luckily, because it was used, I only sunk 900 dollars into it as the guy needed the money. Otherwise it works fine other than an audible internal fan possibly. Sad to hear other people are experiencing the same thing. I just don't know how much money I would want to spend to get things repaired... things like this annoy the heck out of me...
Has anyone replaced the display and seen if this helps?? Im considering it because this unit's dead pixels, if I could kill two birds with one stone, that would be great.