Difference in behaviour with --backup

[va_public <yahoogroups at vikas.mailshell.com>]

--- In rsync at yahoogroups.com, "va_public <yahoogroups at v...>" 
<yahoogroups at v...> wrote:
> When I do
> 
> rsync -av --backup --backup-dir=/dir1/dir2/Backup \
>  /dir1/dir2/dir3 machine:/dir1/dir2/dir3

Sorry, yes, I did give the trailing '/' after my source dir name 
i.e. /dir1/dir2/dir3/