Originally Posted by TerryK
Unfortunately, most of the web sites are not designed for tabbed browsing. They only recognize one session from your computer. Therefore, when you click on cancel in step 9, it cancels the most recent itinerary opened in step 6.
Which of course is horrible web form design. If the cancel confirmation form is submitted at a later point when the latest viewed reservation for the session has changed, it should return an error rather than canceling the wrong reservation. This can easily be done by including a hidden field containing a reference id to the reservation that the cancel confirmation page was loaded for, or keeping a more detailed track of activity on the server-side.