I’ve noticed on OS X that if I’m scrolling in the window and move the mouse out of the active window before the scroll finishes, the scrollbars remain on the screen, they do not fade out. If I scroll and don’t move the mouse until the scroll is finished, the scrollbars appear and fade as expected.
I’ve noticed this in 2.0.1 stable, dev and nightly build, and in all the 3.0 builds with the overlay setting set to system or enabled (disabled, of course, always shows the scrollbars).
Not a big deal, but strange if it’s using OS X’s API.