I found this problem with being unable to change Departure Airport and Carrier/Flt No last week, having done it since the system was set up. There is no advice about it on the DHS website but an email to the responsible department (temporarily forgotten its title) elicited confirmation by return that the system had changed last November and that this info was no longer required. ESTAs remain valid for their 2 years unless the Passport details change or a holder's response to one of the Yes/No questions. New ESTAs require some additional information to that sought previously - eg, parents names and POC in the USA.