scrollbar's don't always appear on JLists; swing1.1.1beta1

I have a JList, which in the course of its life gets bigger.
The list is contained in a JScrollPane.
The list uses a subtype of AbstractListModel, and I am calling
fireIntervalAdded when the new elements are found. This is
apparent because they display in the list. If at this point
the list is now too big for the viewport, then scrollbars
appear. This is good, so far...

However, if the list gets bigger and still fits within the window,
and I then shrink the window, then the scrollbars don't appear
until I make it smaller than the original size of the list.

In other words, the scrollpane does not seem to be noticing that
the list got bigger, in this case.