File save upload doesn't replace existing file despite FILE_EXISTS_REPLACE

I'm trying to force replacement of existing file with same name, if a new version is uploaded by user. I've seen a lot of posts about this topic but none that I could find addresses how to force the replacement.

I'm using a custom form, and here's the code I've been trying to make work during the form validation:

  $file = file_save_upload(
      'file', 
      array(
        'file_validate_is_document' => array(), // Validates file is really a document.
        'file_validate_extensions' => array('pdf doc ppt pps avi mpg mov wmv'), // Validate extensions.
      ),
      'public://',
      FILE_EXISTS_REPLACE
  );

The revised file (let's say "file.jpg") is uploaded, but inevitably Drupal creates a new copy and renames it file_0.jpg, file_1.jpg, etc for each new version.

I even tried to programmatically delete the original file using "file_delete" prior to committing the upload but I still get the copy!

Any help would be appreciated.