Hi Shai,
I found the cause: I misunderstood the purpose of getListFocusComponent() method of ListCellRender.
My intention was to have a List confirm selection of an item by providing a focus component.
Although this did result in the desired effect, the actual purpose of this component is to allow for keyboard navigation.
In this context it makes sens that clicking below the list places focus on the first item.
Sorry to have wasted your time.