When scrolling pages vertically, Navigator only shows first pages, no scroll bar

1. In Preferences > Canvas > Scroll Pages, select "Vertically."
2. Display Navigator.
3. Adjust Navigator width, if necessary, so that it can't show all of a given score at once.
4. Page through the score to any point beyond the first few pages showing in the Navigator.

Expected result: The Navigator view shows the current location, highlighted with blue rectangle, and allows you to change location by scrolling through the Navigator view and clicking elsewhere.

Actual result: The Navigator view is stuck at the top with the first few pages, and will not show anywhere else. Notice that the scroll bar is immobile at the bottom of the Navigator, rather than enabling scrolling vertically.

In this screenshot, there is no blue rectangle in the Navigator at all, demonstrating that it isn't showing the current location.