time interval shifts in calendar display

When I'm in Calendar, I see a certain time interval, depending on screen size. In the first example below, it goes from 07:00 to 21:00. When I toggle between Calendar and Email tabs (using shift+tab or by mouse-clicking) and back to Calendar, the time interval now shows 06:15-20:15. (second image) If I toggle once more, it starts at 05:15, and so on, it goes back one hour after each toggle, until it reaches 00:15. This is very annoying because I have to constantly toggle between Email and Calendar, so the Calendar is more and more shifted and I have to move it manually to keep working. I haven't seen this bug described before. Do other people experience it? Any solutions?

Thanks, Franck