We are aware of some navigational inconsistencies when users are view the site in 'Private Browsing' mode on the ipad. This may also be evident when using private browsing in other browsers.
Private Browsing turns some of these services off on your local device which can result in the website not storing 100% of that information all the time.
The only solution in this case is to turn OFF private browsing for your ipad when using this website. You can turn this on and off from the general settings in your ipad or mobile device. See the image below as an example from the ipad.