Interesting and weird.
The menu command you refer to is displayed in the Key Commands dialog as Zoom Tracks Exclusive. I know that command, and want never to use it. But what you describe it doing is what it’s meant to do.
So it’s a typo, or it’s a bug if the wrong command it attached to the menu item, but I don’t know which command, since Zoom In Tracks does zoom the selected track.
Check out Enlarge Selected Track. I think it’s more in line with your expectations. A great way to learn what’s available is by reading the list of Key Commands. There are tons, since their market base is so diverse after 35 years.