I was using the ProBlog add-on on my site and had a page list on the home page that showed the 4 most recent posts. When I upgraded to C5 5.6.1.1 from 5.6.0.2, the blocks would disappear and reappear both in edit and in user modes. When I was able to see them in edit mode, I tried to delete them, they would appear to go, then they would reappear after a couple of refreshes. When I tried to edit them, it said the block could not be found and if they had been moved to refresh the page. I replace the core concrete directory and all was made better. Here is the site:http://stepwise-marketing.com