Thank you so much, Chris!  That solved the problem.  I don't think I would have thought but it makes logical sense.

I have two WebDatePickers to select a date range which I initialize with pre-selected dates.  When the dates are changed I have it reloading a WebDataGrid.

I'm using the WebMonthCalendar 's OnSelectedDateChanged  like described in the post above with the AutoPostBackFlag-ValueChanged set to "On"  to get the selection of a date in the calendar to automatically post back and change the contents of the grid.  However, I'm getting an annoying behavior.  When initially running the application, the first time I click on the arrow to display the month calendar drop down, a post-back occurs and the calendar does not display.  Any subsequent clicks on the arrow do not cause a postback and the control works just fine as I had expected.  I currently have the EditMode of the WebDatePicker set to "CalendarOnly".  If I do not set this and allow the user to change the date manually by typing in the edit box, the annoying behavior returns upon once again clicking on the arrow to display the calendar.

Is there anything I can do to keep this unneeded initial postback event from firing? 

Thanks.