I have attached a sample console app (Telerik assemblies removed to meet file size) that shows the issue. The End By (UNTIL in the pattern) is not included in the occurrences. I tested this scenario in Outlook per advice from the support ticket and the End By parameter is inclusive in this case. The spec also seems to indicate that the End By/UNTIL is inclusive:

The UNTIL rule part defines a date-time value which bounds the
   recurrence rule in an inclusive manner. If the value specified by
   UNTIL is synchronized with the specified recurrence, this date or
   date-time becomes the last instance of the recurrence.