The function [file_unmanaged_copy][1] in Drupal core calls `drupal_set_message` on certain conditions; even with visible errors messages disabled, anonymous users see this. Indeed, the comment in the code even has a TODO to change it to an exception.

Obviously I don't wish to hack core, so is there a clean way to supress this for anonymous and non-admin users?

Notably, the message is in a `t()` function, so I could use the [stringoverrides][2] module, but this would affect all users, including site administrator so it's a bit problematic.


  [1]: https://api.drupal.org/api/drupal/includes!file.inc/function/file_unmanaged_copy/7
  [2]: https://www.drupal.org/project/stringoverrides