Archiving to vfat

[crateman.universalistic356 at aceecat.org]

I am trying to use rsync between two local directories on Linux.

The source directory is on a normal ext4 partition, under my home
directory. The destination is an SD card that I insert into the card
reader on the computer, formatted with a vfat filesystem.

The command line is like

  rsync -avC --delete /home/itz/foo/ /media/itz/DEAD-BEEF/foo/

This does not work as I expected: all files are always transferred,
even when I run this command 2 times with nothing in between. I
expected only new or changed files to be transferred. Is this

- a user error
- a rsync bug
- a limitation of the vfat filesystem?

In any case, what can I do, using rsync or possibly something else, to
do what I want? I note that the absolute timestamps on the files are
unimportant; I can change them to whatever. All that matters is that
new and changed files are copied every time I run this command, and
only those files.

-- 
Ian