If there is already a file named archive.tar.gpg (or archive.tar.sig) and you try to create a new encrypted (or signed) archive with the same name, then Kleopatra asks whether you want to overwrite the existing file or change the name of the new file. There is also a button to suggest a new file name. Pressing this button will suggest the name archive.tar (1).gpg (or archive.tar (1).sig).
The problem with this suggestion is that Kleopatra doesn't recognize archive.tar (1).gpg as encrypted archive, but just as plain encrypted file.