I used the admin UI to change the backup target from /opt/zimbra/backup to /opt/zbackup. The sessions backups are now landing in the new target directory but ldap backups are still going to the original. I haven't seen any posts or bugs about this.
Here's the target directory's ls -l output:
I'm using 4.5.9 with Ubuntu 6.10
drwxrwsr-x 5 zimbra zimbra 4096 2007-10-25 08:40 zbackup
I can post a bug if it is one. Meanwhile, I'll just deal with it by making /opt/zimbra/backup a symlink to my intended target.