Comment 4 for bug 365915

Well, if nothing else I believe I've pinpointed the relevant error message

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 Backing up /etc/ldap/slapd.d/ in /var/backups/slapd-2.4.11-0ubuntu6.2... done.
  Moving old database directories to /var/backups:
  - directory dc=nodomain... done.
  Loading from /var/backups/slapd-2.4.11-0ubuntu6.2:
  - directory dc=nodomain... failed.

Loading the database from the LDIF dump failed with the following
error while running slapadd:
    slapadd: line 29: database (dc=nodomain) not configured to hold "dc=api,dc=no"
    slapadd: line 29: database (dc=nodomain) not configured to hold "dc=api,dc=no"
dpkg: error processing slapd (--configure):
 subprocess post-installation script returned error exit status 1
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Will have to get back to you on the how and why. Not that familiar with the slapd package. (yet)