[horde] Can not create additional address books

[Bjoern Voigt]

My Horde Groupware Webmail 5.2.7 setup currently does not show the
"plus" icon to create additional address books. Each user has only
one address book. But creating new calendars works.

My Setup
o Horde Groupware Webmail 5.2.7
o Turba backend configuration horde/turba/config/backends.local.php

<?php
$cfgSources['localsql']['use_shares'] = true;
$cfgSources['localldap']['use_shares'] = false;
$cfgSources['localldap']['disabled'] = false;
$cfgSources['localldap']['title'] = 'My LDAP global address book';
//...
?>

o Turba configuration  horde/turba/config/conf.php
<?php
$conf['menu']['import_export'] = true;
$conf['gal']['addressbook'] = '<a-long-id>';
$conf['shares']['source'] = 'localsql';
$conf['comments']['allow'] = true;
$conf['documents']['type'] = 'horde';
$conf['tags']['enabled'] = true;
?>

What could be the cause?

Greetings,
Björn