--backup-dir confusion

[Philip Mak]

With the following rsync settings:

cd /home/lina_backup
rsync -R -v -z -rlptgo --delete \
  --password-file=password \
  --include-from=include --exclude="*" \
  --backup --backup-dir=./`date -d yesterday +%Y-%m-%d` \
  rsync://root@lina/backup current

I would expect the backup directory to be /home/lina_backup/2001-12-29.
But it becomes /home/lina_backup/current/2001-12-29. Is this a bug? (Am I
abusing the rsync command by trying to use relative paths and shouldn't do
this?)

BTW, will my settings clobber a file if something goes wrong with the
rsync? Or will the existance of the backup directory make certain that if
the rsync doesn't work, it at least keeps the older copy of a file?