I'm quoting this as a timely reminder. Even more counterintuitive is that, once an alert has been set for a flight, clicking on the magnifying glass returns "did not detect a flight schedule change" for flights that have been cancelled.
Because, normally, a canceled flight doesn't result in a change to the published schedule. The schedule alert is using the Flight Details search. Our plan is to add a separate Flight Status alert at a future date. How the Quick Check works isn't counter intuitive, it's just checking the alert in the same way the alert check itself does, so it wouldn't result in anything different.