Any update marlon bishop or anyone having the same problem? I too have the same issue with my 2.8GHz/16GB/1TB/750m 15" rMBP Mid-2014 since the macbook pro came out last July. I see something very similar when web browsing to your screen shot above which will occur and essentialy pop up where I have recently closed a pop-up window playing video in the corner and once closed a shadow artifact of the window will flash like crazy on and off with the same kind of numbers and letters and strange lines within it where the video was playing. The cursor will also flash on and off as if I'm clicking many times a second! If I open a new window the artifact will appear on that new window as well, only way to get rid of the artifact is to close the original window before the errors occurred and start afresh.
This seems to be only occurring on the 2.8gh mid 2014 macbooks?? This also only happens using Safari as never happens while using Chrome. I prefer Safari so wish I knew why this was happening.