Expand drop down height/make scrollbar visible

When adding users to a user group (and in other places where you can use listboxes with a multi-select), choose 3 items and the 4th becomes hidden from view.

As shown here, I’ve selected 3 users, now I want to include a 4th. I’ve filtered down to “sap” but it only shows the 3 previous selections. There’s no scrollbar to let me know there’s a selection down below. You have to have a very good eye to see the opaque item.

After scrolling I see:

We should make the height of this listbox expandable and make the scrollbar visible to let people know.