@jomaxro Based on my testing locally, this only happens when you’ve already loaded the page with the stream of bookmarks and someone removes your permission to view one of the posts in the stream. Once you refresh the page, the stream will no longer include the bookmarks.
This is not easy to implement from what I’ve gathered. There are many actions that can result in a user losing permission to a topic/post and we need to have those actions publish updates to the clients. Our topic list actually works this way as well, only new topics are pushed to the clients but a topic that has been deleted will still remain in the stream and clicking on it will direct the user to a topic not found page.
In order to make it less confusing, I’ve submitted a PR to allow a user to remove their own bookmarks even if permission to see the post has been removed.