Using gnome-calendar 42.1-40-1-x86_64, scrolling with the mouse wheel in Month view silently changes the month without redrawing the calendar. I can tell the month changes in memory because clicking on the arrow keys redraws the interface.
For example, today is September. Mouse wheel down twice, and the display continues to show September, but click on the right arrow, and suddenly I'm seeing December's calendar.
This does not appear to be affected by which calendars, if any, are actually toggled on.