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Calendar events - Dublin VTIMEZONE is wrongly defined and misinterpreted in Android using DAVx5

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I am working with Thunderbird 60.5.1 and Lightning 6.2.5. I have noticed that events created in Lightning synchronize and display correctly to the web interface of my email provider. Nevertheless, my phone (Android 9, LineageOS 16.0) is unable to display the time of the event correctly. The events are synchronized with the latest DAVx5 Adrdoid app using Caldav. Each event I create for today using Thunderbird, is displayed on the phone as an event for 22:00 yesterday, regardless of the actual event time.

I asked a question regarding this problem at the DAVx5 support forum where they investigated the app synchronization logs and concluded that the VTIMEZONE definition from Thunderbird is wrong for timezone Europe/Dublin. Here is the thread: https://forums.bitfire.at/topic/1985/bug-related-to-parsing-time-or-timezone-of-events-created-with-thunderbird-lightning

The problem does not arise when I create an identical event using the Europe/London timezone which in reality is identical to Dublin.

Here is the timezone definition that is attached to the events created in Thunderbird.

BEGIN:VTIMEZONE TZID:Europe/Dublin BEGIN:STANDARD TZOFFSETFROM:+0100 TZOFFSETTO:+0000 TZNAME:IST DTSTART:19700329T010000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3 END:STANDARD BEGIN:DAYLIGHT TZOFFSETFROM:+0000 TZOFFSETTO:+0100 TZNAME:GMT DTSTART:19701025T020000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10 END:DAYLIGHT END:VTIMEZONE

It says that IST (standard time) switches from an offset of +0100 to +0000, and GMT (daylight time) switches from +0000 to +0100. So GMT would have an offset of 0100 to itself (because offsets are given relative to GMT), which is clearly wrong (https://en.wikipedia.org/wiki/Time_in_the_Republic_of_Ireland).

In the Thunderbird definition, standard time starts on the last sunday before March and summer time just before October. This is wrong, too. According to https://github.com/ical4j/ical4j/blob/cd29ee1884dac701eeb1680582d5718b7f0f6258/src/main/resources/zoneinfo/Europe/Dublin.ics, it’s just the other direction.

I am working with Thunderbird 60.5.1 and Lightning 6.2.5. I have noticed that events created in Lightning synchronize and display correctly to the web interface of my email provider. Nevertheless, my phone (Android 9, LineageOS 16.0) is unable to display the time of the event correctly. The events are synchronized with the latest DAVx5 Adrdoid app using Caldav. Each event I create for today using Thunderbird, is displayed on the phone as an event for 22:00 yesterday, regardless of the actual event time. I asked a question regarding this problem at the DAVx5 support forum where they investigated the app synchronization logs and concluded that the VTIMEZONE definition from Thunderbird is wrong for timezone Europe/Dublin. Here is the thread: https://forums.bitfire.at/topic/1985/bug-related-to-parsing-time-or-timezone-of-events-created-with-thunderbird-lightning The problem does not arise when I create an identical event using the Europe/London timezone which in reality is identical to Dublin. Here is the timezone definition that is attached to the events created in Thunderbird. BEGIN:VTIMEZONE TZID:Europe/Dublin BEGIN:STANDARD TZOFFSETFROM:+0100 TZOFFSETTO:+0000 TZNAME:IST DTSTART:19700329T010000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3 END:STANDARD BEGIN:DAYLIGHT TZOFFSETFROM:+0000 TZOFFSETTO:+0100 TZNAME:GMT DTSTART:19701025T020000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10 END:DAYLIGHT END:VTIMEZONE It says that IST (standard time) switches from an offset of +0100 to +0000, and GMT (daylight time) switches from +0000 to +0100. So GMT would have an offset of 0100 to itself (because offsets are given relative to GMT), which is clearly wrong (https://en.wikipedia.org/wiki/Time_in_the_Republic_of_Ireland). In the Thunderbird definition, standard time starts on the last sunday before March and summer time just before October. This is wrong, too. According to https://github.com/ical4j/ical4j/blob/cd29ee1884dac701eeb1680582d5718b7f0f6258/src/main/resources/zoneinfo/Europe/Dublin.ics, it’s just the other direction.