--compare-dest not working for me. what am I doing wrong?

[Lucas Meijer]

Hey Matt,

> Relative --*-dest paths are interpreted relative to the destination
> directory (as stated in the man page), so you should use:
>
> rsync -av --compare-dest=../b a/ c/
>   
tried that too, same result for me:

mkdir a b c
echo foo > a/test
echo foo > b/test
rsync -av --compare-dest=../b a/ c/

expected: no copy
actual result: a/test gets copied to c/test

(also tested with --compare-dest=../b/ --compare-test=/b/, and the other 
things I actually tried I'm to emberrassed to write here :) )

Bye, Lucas