Calendar day view takes a time as input parameter. While day view purports to show the calendar for the day, it actually only shows events from the timestamp provided onwards (although the time provided is not displayed). This is massively confusing for students, and has caused some to miss lectures.

The logic around timestamp calculation at the start of calendar/view.php is contorted and not obvious. I assume that in introducing this behaviour, the author was primarily considering the "upcoming" view, for which this behaviour would be correct.