1.1.5.
Because the day of the week corresponding to a local time and a UTC time may be different, recurrence rules cannot reliably be expanded using only UTC time.
A meeting occurring every first Monday of the month at 0:30 CEST would be 22:30 every Sunday in UTC. Since the first Sunday of the month is not always occurring just before the first Monday of the month, converting that event to UTC would not expand that rule correctly.