A member of staff entered a date on the 1st of the month using the default values. (without duration, beginning at 00:00 and no repeat)

This event does not show up at all in the calendar, in sideblock or in calendar upcoming events.

The same problem occurs with any event set to begin in the first hour of the first day of the month (up to 00:55). If I set the event to begin at 01:00 then it shows up fine.