event is raised when an Insert button within a Details View control is clicked, but before the insert operation.This allows you to provide an event handler that performs a custom routine, such as canceling the insert operation, whenever this event occurs.A Details View Insert Event Args object is passed to the event handler, which allows you to indicate that the insert operation should be canceled.
Actually it’s not an issue; this is default behavior of Share Point 2010 Document Libraries.
This happens only at the time of uploading file in to library.
I have explained the scenario below So, the custom event fires twice only at the time of uploading file into library.
The first time the Item Updating and Item Updated events fire it is in response to the document properties changing.
The second time they fire it is in response to the document being checked in.
It appears as though they are firing twice in this situation because Share Point is updating the properties on the document and then checking it in on the same request.
If you were to check the document out and edit the properties on the document, you would see the Item Updating and Item Updated events fire once.
Later on, when you checked the document in, you would see those events fire again.
So the double-event firing isn’t a bug, it’s just a result of the automatic check-in that occurs when you first add a document to a document library.