Thanks. One idea for a work-around I just had is to create two lists, one with pbScroll True and one with False. Then we just show the applicable list.
Kludgy, but better than nothing. We'll probably do that for now.

Our use case is that we have customers with (optional) departments. Some have none, some have a handful, and some have hundreds.

When they order, they can select which department to order to. If a customer has none, we hide the list. If the customers has hundreds, we show a normal scrolling list with maybe 10 rows. But a very common case is that the customer has 2-3 departments, in which case the scrolling list is mostly empty, and wastes very much precious vertical space.