Steps to reproduce:
1. Run any swing application with combobox
2. Click on combobox to show popup
3. Mouse wheel on it.
Popup will close unexpectedly.
Selection should change
It is actually normal to get the mouseWheel event on the window
in case the scrollBar is invisible.
When JScrollPane can't scroll it doesn't consume the mouseWheel event
and the Swing popup is closed on every other platform.
Another serious problem is found -
when the scrollBar is visible it is impossible to scroll it
with the single turn of the wheel.
It gets scrolled only if you rotate the wheel fast enough.
Reproducible, for some reason we get two MouseWheelEvents.
The second one is targeted for the window and BasicPopupMenu.MouseGrabber.inInPopup() returns false and closes the popup.