How to reproduce
- Open calendar, go to month view
- Create a two day event (e.g. by drag-start on day one and drag-stop on day two
- In event form make sure you have set it to da day event (without hours) and the end date is one day more than the start date
- Save event
- => NOK: event is displayed as a one day event
In 12.5 the behaviour is still correct.