2.1.5 [RFC5545] Section, DTEND MUST Be Later in Time Than DTSTART

The specification states, "The value type of this property MUST be the same as the 'DTSTART' property, and its value MUST be later in time than the value of the 'DTSTART' property."

Outlook can export iCalendar objects that have the same values for DTSTART and DTEND.