Laptop Calendar app changes visible hours

The apple calendar app [on laptop] changes the number of hours showing, when in the background.

I set it to show 16 hours per day. That works. Then i go to other apps, and when i come back to the calendar app, it shows fewer hours, perhaps 14 or so. The preferences are still set to 16. If i change the preferences setting, the view jumps immediately to the new number of hours, fine. But if i click away, then return, the visible hours will have changed again.

Anybody else?