I can't reliably reproduce this, but occasionally I find stars' clickable area, or the area that responds to mouseovers, is smaller than it should be. One time, the star was only clickable on half its visible vertical height. More frequently, a star will be online clickable / respond to mouseovers in a vertical range of a pixel or so in height, for a 30+ pixel high star on screen. Which star is affected seems to change randomly when zooming or scrolling, though it always seems to be just one star at a time. Unexplored stars are definitely affected, though I'm not sure about explored stars.