When you add items to an empty Spinner it will changed the selected item to the first in the list, but there is no ItemClick event to indicate the selected item has changed.
Just trying to keep things equal. If a Tab changes by code it still sends the TabChanged event. The Spinner event may be in a Class or something too that isn't aware that the list was updated causing the selected item to change. Should be a simple check to see the selected item before and after adding an item to the list and if different send the event.