the redirect in the update does not specify a page, only a folder?
the page you sent is an index page, but there is no indication of where the page resides in your site.
Is it the index page in the itinerary_added/ folder that the update is redirecting to? if so, that explains why the insert is happening twice.
I would make sure that the redirect on the up date is pointing to another page.
also, in some server configurations, when a header function call is used to redirect the page, it will execute the rest of the code on the page before the redirect is executed.
to prevent this, edit: