I'm attempting to use this to back up a (Joomla) website from the hosted remote web server to a local server hard disk, but obviously I do not wish to recopy files which have not changed.

So I've used
Edit -> Settings -> Transfers -> File exists action -> Default file exists action -> Downloads -> Overwrite file if size differs or source file is newer
Whew!

However, it seems to me that, in spite of this, every file is being copied down to the server, whereas very few should be.

I can't find a mention of this problem anywhere - and, yes, the website server has almost exactly the same time as my local server (within seconds)

Can anyone who uses FileZilla help me here? Thanks!