I was talking only about the contents of a particular file in ical4j repo. It looked like it contained incorrect timezone definitions. However, right now I can’t reproduce the problem I mentioned. An event created either on the server or on the client syncs to the other party with the correct timezone in both ways.
I vaguely recall that earlier after wiping calendar storage the events would be synced with incorrect timezones, so I’ve just tested it. Unlike Google calendar, the events synced by DAVDroid were not repopulated, but after I deleted and re-added the account everything was back in place, including the proper timezones.
I guess this particular issue is resolved.