Thunderbird 115.9.0 (64-bit). I have my timezone set to manual, Europe. I create an event for 30 March 2024 and the time is displaying in my time zone I mark it as ALL DAY and it switches to Local Time (not a problem so far) If I display the calendar as 1 month starting with 24 March, then the event shows properly on Saturday 30 March If I scroll the calendar up to start on 31 March, '''now the event shows on 31 March'''. If I edit the event, it says the timezone is Chicago. Changing the timezone and resaving it doesn't help.