"the following files are not valid" list contains mostly valid files

I’ve been experiencing a strange problem for a very long time with CIS:

The File List menu under File Rating contains about ~1000 items. If I clean it it comes back after a few days to a similar number. The strange thing is that if I click the purge button a window appears listing hundred of files. The window subtitle is “The following files are not valid”. The problem is that most of these files do exist and are thus valid…

Is there something wrong with my config or is this a known issue?

File list also keeps track of file hashes, so if a file gets updated which changes the hash, the older version is no longer valid as it doesn’t exist anymore. That is why you can see duplicate entries in the file list of files of the same file path and file name. For example when the web browser you use is updated, you will have two entries of the same executable until you purge the file list.