Thank you very much for giving the solution.

I wanted a file for each save. I've done it using timestamp in format yyyymmddhhmmss.
(attention: if system date is changed, it's possible some files to be overwritten)

//---------save-backup.bsh------------

import java.util.Calendar;
import java.text.SimpleDateFormat;

//backup path
BackupPath = "Z:\\Jedit_backups\\"; //don't forget the trailing \\

Calendar cal = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmss");
timestamp = sdf.format(cal.getTime());


path = buffer.getDirectory();
path = path.replaceFirst("ftp://", "");
path = path.replace('/', '\\');
path = path.replaceAll(":", ""); //this is for local files (c:\ -> c\

//todo : remove other unwanted characters ?

path = BackupPath + path;

(new File(path)).mkdirs(); //create the backup directory if it doesn't exist


path = path + buffer.getName() + '_' + timestamp;
// buffer.getLastModified(); - fails for FTP: puts 0 all the time

buffer.save(view,path,false); //save copy
VFSManager.waitForRequests();
buffer.save(view,null,true);

//Macros.message(view, "Backup done in " + BackupPath);
view.getStatus().setMessageAndClear("Macro save-backup.bsh: Backup done in " + BackupPath);

//--------end

- put this in a file, eg save-backup.bsh
- put the file in a subfolder (eg Files) of 'macros' folder from jedit installation
- open jedit
- Utilities > Global Options > Shortcuts
- enter, in the 'filter' field, the name of the file
- click in the 'Primary shortcut'
- press CTRL + s (the 'Save' shortcut)
- accept the override
- in 'Saving & Backup' put the 'Max number of backups' to 0 (zero - it disables other backups)
- press OK to save changes
(done in Jedit 4.3)

Ah, well that's disappointing. Thanks for clearing that up though!