Portion of safari window blinking

My wife's Macbook 2011 Pro recently had the logic board replaced due to a known video failure. Since we've gotten it back she's started having a weird problem. In Safari (her primary application...so not sure if it affects the whole system or just Safari).

The problem exhibits itself in a blinking/shifting portion of the active safari window. It's not always on the far left of the window. It's about 150x300 pixels. After a minute or so, it stops.

I can't see how it would be a website problem.

An interesting data point....my wife doesn't like the full resolution screen, so she scales the resolution down to something easier to see.

Any thoughts?