Help with scrollEvent listener

I have a Box in a Panel and a listener for the scrollEvent on the Box. I scroll with the mouse’s wheel in the Panel until the scrollbar reach the top position, but even after it, if I move the mouse wheel, another scroll event is dispatched (or at least catch by my listener so I think it is also dispatched).
How can I see that the last scroll event is a fake (the scroll bar does not move anymore as it does not have where to move)?

Thank you,
Stephanie.