diff --git a/library/Icinga/Application/Web.php b/library/Icinga/Application/Web.php
index 0b3f3f8b8..bb9809479 100644
--- a/library/Icinga/Application/Web.php
+++ b/library/Icinga/Application/Web.php
@@ -84,6 +84,7 @@ class Web extends EmbeddedWeb
             ->setupLogging()
             ->setupErrorHandling()
             ->loadConfig()
+            ->setupLogger()
             ->setupRequest()
             ->setupSession()
             ->setupNotifications()
@@ -97,7 +98,6 @@ class Web extends EmbeddedWeb
             ->setupUserBackendFactory()
             ->setupUser()
             ->setupTimezone()
-            ->setupLogger()
             ->setupInternationalization()
             ->setupFatalErrorHandling();
     }
diff --git a/library/Icinga/Authentication/Auth.php b/library/Icinga/Authentication/Auth.php
index c627ccac0..67a148678 100644
--- a/library/Icinga/Authentication/Auth.php
+++ b/library/Icinga/Authentication/Auth.php
@@ -153,9 +153,20 @@ class Auth
                 continue;
             }
             if (empty($groupsFromBackend)) {
+                Logger::debug(
+                    'No groups found in backend "%s" which the user "%s" is a member of.',
+                    $name,
+                    $user->getUsername()
+                );
                 continue;
             }
             $groupsFromBackend = array_values($groupsFromBackend);
+            Logger::debug(
+                'Groups found in backend "%s" for user "%s": %s',
+                $name,
+                $user->getUsername(),
+                join(', ', $groupsFromBackend)
+            );
             $groups = array_merge($groups, array_combine($groupsFromBackend, $groupsFromBackend));
         }
         $user->setGroups($groups);
diff --git a/library/Icinga/Authentication/UserGroup/LdapUserGroupBackend.php b/library/Icinga/Authentication/UserGroup/LdapUserGroupBackend.php
index bd0835af0..14a9dea67 100644
--- a/library/Icinga/Authentication/UserGroup/LdapUserGroupBackend.php
+++ b/library/Icinga/Authentication/UserGroup/LdapUserGroupBackend.php
@@ -466,15 +466,41 @@ class LdapUserGroupBackend extends LdapRepository implements Inspectable, UserGr
                 );
             }
 
-            $sampleValue = $this->ds
+            $sampleValues = $this->ds
                 ->select()
                 ->from($this->groupClass, array($this->groupMemberAttribute))
                 ->where($this->groupMemberAttribute, '*')
+                ->limit(Logger::getInstance()->getLevel() === Logger::DEBUG ? 3 : 1)
                 ->setUnfoldAttribute($this->groupMemberAttribute)
                 ->setBase($this->groupBaseDn)
-                ->fetchOne();
+                ->fetchAll();
 
-            $this->ambiguousMemberAttribute = ! LdapUtils::isDn($sampleValue);
+            Logger::debug('Ambiguity query returned %d results', count($sampleValues));
+
+            $i = 0;
+            $sampleValue = null;
+            foreach ($sampleValues as $key => $value) {
+                if ($sampleValue === null) {
+                    $sampleValue = $value;
+                }
+
+                Logger::debug('Result %d: %s (%s)', ++$i, $value, $key);
+            }
+
+            if (is_object($sampleValue) && isset($sampleValue->{$this->groupMemberAttribute})) {
+                $this->ambiguousMemberAttribute = ! LdapUtils::isDn($sampleValue->{$this->groupMemberAttribute});
+
+                Logger::debug(
+                    'Ambiguity check came to the conclusion that the member attribute %s ambiguous. Tested sample: %s',
+                    $this->ambiguousMemberAttribute ? 'is' : 'is not',
+                    $sampleValue->{$this->groupMemberAttribute}
+                );
+            } else {
+                Logger::warning(
+                    'Ambiguity query returned zero or invalid results. Sample value is `%s`',
+                    print_r($sampleValue, true)
+                );
+            }
         }
 
         return $this->ambiguousMemberAttribute;
diff --git a/library/Icinga/Protocol/Ldap/LdapCapabilities.php b/library/Icinga/Protocol/Ldap/LdapCapabilities.php
index 5568aa5bb..0e562b115 100644
--- a/library/Icinga/Protocol/Ldap/LdapCapabilities.php
+++ b/library/Icinga/Protocol/Ldap/LdapCapabilities.php
@@ -3,6 +3,8 @@
 
 namespace Icinga\Protocol\Ldap;
 
+use Icinga\Application\Logger;
+
 /**
  * The properties and capabilities of an LDAP server
  *
@@ -347,6 +349,17 @@ class LdapCapabilities
 
         $cap = new LdapCapabilities($connection->cleanupAttributes(ldap_get_attributes($ds, $entry), $fields));
         $cap->discoverAdConfigOptions($connection);
+
+        if (isset($cap->attributes) && Logger::getInstance()->getLevel() === Logger::DEBUG) {
+            Logger::debug('Capability query discovered the following attributes:');
+            foreach ($cap->attributes as $name => $value) {
+                if ($value !== null) {
+                    Logger::debug(' %s = %s', $name, $value);
+                }
+            }
+            Logger::debug('Capability query attribute listing ended.');
+        }
+
         return $cap;
     }