In fact, if the first click before dragging takes place in the upper half of the scrollbar slider, the click is not received nor the drag after. Is like the scroll slider is translated down with half of the slider length (that's why I can drag the slider even when I'm a little bit lower with the pointer). I'll check the click callback and the scrollbar setup functions. Can anybody check if clicking then starting to drag the slider in the inferior half of the slider, even at the top of a file, functions well?