MS Office Add-in (web) doesn't save URL destination inside. For example 1. you add content Add-Id in your document 2. change URL inside (click the link inside it) 3. save it
After you will open your saved document website inside your add-in will be default, not that you have reached before saving
How to fix this error?
i am not sure I get what you are trying to achieve, would be great if you can describe your scenario with more details.
But I can tell you this: Nothing on the add-in state gets saved with the document unless you explicitly save it with it. In order to do that you need to use the settings object. its quite simple to use here are good documentation on how to create and get a setting http://dev.office.com/reference/add-ins/shared/settings
Hope this helps.