Black horizontal lines in Safari
On occasion I see a thin horizontal black line appear in Safari. It's only there on rare occasions and disappears when the page is scrolled.
It tried to make a screenshot whilst the line is on screen but the line is not captured in the screenshot. So it's definitely on my screen but not in the captured screen-data apparently. That's weird imo.
I have Retina MBP mid 2014.
Any thoughts? Solutions?
MacBook Pro (Retina, 13-inch, Mid 2014), OS X Yosemite (10.10.3), Latest Safari