After upgrading from 3.2 to 3.3. Files collection is now just empty in controller when updating entity without selecting new files. So it just removes the file entities. It used to work before 3.3 now it fails.
Maybe I missed something and it's planned changes in form file type behavior?

Here is a demo which shows the issue https://github.com/skornev/vichbundle-sandbox-not-cp-symfony3.3

This issue was raised here dustin10/VichUploaderBundle#776.