On Windows, while dragging the scroll thumb in the bottom filmstrip view, the image thumbnails are rendered, but the informational overlays are not (rating, edit icon, etc.). This is rather annoying, since when I am scrolling, I more often am looking at those overlays than the image thumbnails themselves.
Mouse-wheel does work as expected, but does not smooth-scroll the thumbnail view, so it is easy to lose track of where you are in the list of images.
There seem to be many cases in the app where rendering is blocked when the mouse button is down on a control, which is unfortunate, and makes the app feel much less responsive than it otherwise could.