The migration script system 13-to-14 executes find /usr/share/zoneinfo/posix -type f -or -type l | sed -e s:/usr/share/zoneinfo/posix/:: to find a list of valid timezones. This command only returns the first level of the timezones (continent etc.) resulting in the migrator changing valid timezones to UTC.
We should update the migrator to use systemd-provided command timedatectl list-timezones to get a valid list and prevent valid timezones being mistakenly changed.