Users can see Newsfeeds from pages they follow even without access permission to the page.
When a user follows a page and afterwards his access permission is revoked he can still see all old and new messages of this site.
I found this technet article: https://technet.microsoft.com/en-us/library/dn167721.aspx
If a user’s permission to a URL changes from access granted to access denied within the long TTL cached period, the feed item will still appear in the user’s feed. However, the user will be unable to open the URL because SharePoint security prevents users from accessing information that they do not have permission to. After the long TTL period expires, the security trimming process repeats and the cached item will be updated to access denied so the feed item no longer appears.
I tried to fix this by setting the "SecTrimCacheMaxTTLMinutes" to one hour but the new and old messages still appear 10 hours later.
Is this a known Newsfeed bug or could it be a problem with the "User Profile service application"?