Hi Linda,
It may be possible that when the user clicks the favourites link, the browser serves cached content. If the specific functions use AJAX, a request is made to the server which is rejected because the user isn't logged in. I very much doubt that the user needs to also remove the link, unless they didn't create a favourite, but tried to save an offline version and linked to that.
I would advise you to ask the users to carefully reproduce the steps they took to add the bookmark, and see whether they do anything odd.
It may be possible that when the user clicks the favourites link, the browser serves cached content. If the specific functions use AJAX, a request is made to the server which is rejected because the user isn't logged in. I very much doubt that the user needs to also remove the link, unless they didn't create a favourite, but tried to save an offline version and linked to that.
I would advise you to ask the users to carefully reproduce the steps they took to add the bookmark, and see whether they do anything odd.