I have a combo box with a list of items. When I open the combo box popup and try to scroll using the mouse wheel (my mouse pointer is on the combo box and not on the combo box popup), the popup gets closed. If the combo box popup has a vertical scroll bar and then if the mouse pointer is inside the popup and if I try to scroll using mouse wheel, it works fine: the popup doesn't get closed. However if the popup doesn't have a vertical scroll bar (ie., less items say 4-5 items) and then even if the mouse pointer is inside the popup, on wheel scrolling the popup hides.
This issue is somewhat related to http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7141296 but not completely fixed even in latest JDK7_45.