MBP 17" 2010: horizontal lines extending out from open windows on 30" ACD?

Question

I have a mid-2010 17" I7 with anti-glare screen. The topcase was replaced for factory damage and now the screen was replaced by Apple here in Paris, where I live. I use the MBP with a 30" ACD at home, with no problems until I picked up the repaired MBP yesterday with new screen. I now notice that when I open a window, like Safari or Mail, the lines (let's call it the lower line that frames the menu bar in grey on the top of each open window) seems to extend beyond the open window and run across the top of the entire 30" display. If I move the window, that line moves across the screen with it. It doesn't occur on the MBP screen itself, only on the attached 30". So that if you open Safari and place it in the center of the external display, you see the line running from the grey menu bar on top of the window extend out in both direction across the entire display. It has no effect within the windows you are looking at all, but this wasn't there, or I never noticed it before. I changed the desktop background to see if it changed, and basically not, except it is not viewable so much with light or white background.
There is no effect within the windows being viewed. It's as if the line running out from the frame of the window, especially the bottom part of the grey menu bar on top, are extending out across the screen.
Any suggestions would be greatly appreciated.

Answer 1

It turns out that I tested my 30" ACD with a friends Macbook and it has the same phenomenon. It's quite strange. The darker the blue or grey the more this line flows out from the grey bar frame on Safari or Mail windows. The smaller the window the less evident the phenomenon. Again, it has no effect on the windows themselves, and only occurs toward the top of the display. When you move the window down on the screen it disappears. And it is only the line below the grey upper bar that is rather bold that bleeds out across the screen.
I wonder if there is a way to reset the display or move to some default setting that would correct this.