When dialog appears asking to overwrite file, it allows choosing "append" as one of the possibilities.
As pointed out in forum (http://forum.copyhandler.com/general-support-(english-only)/what-does-'append'-mean/), the naming is a bit unfortunate as appending might mean different things:
- append the whole source file to the existing part of destination file, or
- appending the remaining part of source file to the destiantion file, or
- resuming copying (which is the exact thing happening).
Change the naming of the "Append" button to something more precisely describing the operation.