"All day" events start and end at 01:00 instead of 00:00

[logological]

I'm using DavMail 6.2.2 with Thunderbird 115 on openSUSE Tumbleweed. My system's timezone is set to America/Winnipeg (which is Central Time), and Thunderbird is configured to use this system timezone.

If I create a new event in Thunderbird and check the "All day Event" box, then I expect it to begin at 00:00 on the start date and to end at 24:00 on the end date. However, for DavMail calendars only, Thunderbird shows these events as beginning at 01:00 on the start date and ending at 01:00 on the day following the end date.

Perhaps this problem is related to Issue 342.

[logological]

Interestingly, if I edit the all-day event once it's been created, I see that the "All day Event" box is unchecked, and that start and end times of 01:00 are explicitly given in the start and end date fields. If I re-check the "All day Event" box, correct the end date, and re-save the event, then this time the event is saved with the correct starting and ending times. So it seems it's only when all-day events are initially created that this problem arises.