I run into this same issue on both a 1x and retina display on Yosemite. Losing the visual affordance between sections make the source list slightly harder to use - but it all adds up :)
I keep telling Alex this. :P
Some weird stuff had to be done so it wouldn't look horrible on Yosemite (transparency and whatnot, IIRC) and the shadow's no longer there. Fingers crossed.
I run into this same issue on both a 1x and retina display on Yosemite. Losing the visual affordance between sections make the source list slightly harder to use - but it all adds up :)