Very strange behavior when creating certain custom recurrences on events. Give this a try.
Display any CRM contact record and create a new event.
Set the date to May 4 (first Monday in May)
Set a recurrence with these properties
Repeat Type = Custom
Frequency = Monthly
Repeat on = First: Monday
Ends after 2 times (any number is fine even 1)
Click Done (in the recurrence dialog) and observe the starting date. It is now June 2 (the first TUESDAY in June). Click Save. The event is NOT scheduled in June at all but on the first Monday in July.
This works with other dates as well, and sometimes it works as designed.
Scott Holmes