This is only an issue on platforms that call handleMouseDoubleClickEvent (like Mac). The scrollbar needed to get sent the release event on the second click so it knew it wasn't dragging any more.
Created attachment 23669 [details]
Comment on attachment 23669 [details]
The patch looks good. But I do think you could make a regression test of it. If it is not possible, now, we should consider making it possible/easier in the future. With tons of scollbar changes, it would be a shame not to test going forward.
Fixed in r36783.