diff --git a/CHANGELOG.md b/CHANGELOG.md
index cb7d109eb22..bc9f2275c21 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@
 - Password: Add ldap_samba_ad driver (#8525)
 - Password: Allow LDAP access using LDAP URI and SASL binding (#8402)
 - Fix potential HTTP protocol version mismatch (#8982)
+- Fix bug where installto.sh/update.sh scripts were removing some essential options from the config file (#9051)
 
 ## Release 1.6.2
 
diff --git a/bin/update.sh b/bin/update.sh
index 8db7d8b92cf..5728658b960 100755
--- a/bin/update.sh
+++ b/bin/update.sh
@@ -88,7 +88,7 @@ if ($RCI->configured) {
             if (!empty($opts['accept']) || strtolower($input) == 'y') {
                 $error = $written = false;
 
-                echo ". backing up the current config file(s)...\n";
+                echo "- backing up the current config file(s)...\n";
 
                 foreach (['config', 'main', 'db'] as $file) {
                     if (file_exists(RCMAIL_CONFIG_DIR . '/' . $file . '.inc.php')) {
@@ -100,7 +100,7 @@ if ($RCI->configured) {
 
                 if (!$error) {
                     $RCI->merge_config();
-                    echo ". writing " . RCMAIL_CONFIG_DIR . "/config.inc.php...\n";
+                    echo "- writing " . RCMAIL_CONFIG_DIR . "/config.inc.php...\n";
                     $written = $RCI->save_configfile($RCI->create_config(false));
                 }
 
diff --git a/program/include/rcmail_install.php b/program/include/rcmail_install.php
index 5adcfe3fe93..70877dd5ada 100644
--- a/program/include/rcmail_install.php
+++ b/program/include/rcmail_install.php
@@ -435,10 +435,10 @@ public function merge_config()
                 else {
                     $this->config[$replacement] = $current[$prop];
                 }
-            }
 
-            unset($current[$prop]);
-            unset($current[$replacement]);
+                unset($current[$prop]);
+                unset($current[$replacement]);
+            }
         }
 
         // Merge old *_port options into the new *_host options, where possible
@@ -460,9 +460,9 @@ public function merge_config()
         }
 
         // add all ldap_public sources having global_search enabled to autocomplete_addressbooks
-        if (is_array($current['ldap_public'])) {
+        if (!empty($current['ldap_public']) && is_array($current['ldap_public'])) {
             foreach ($current['ldap_public'] as $key => $ldap_public) {
-                if ($ldap_public['global_search']) {
+                if (!empty($ldap_public['global_search'])) {
                     $this->config['autocomplete_addressbooks'][] = $key;
                     unset($current['ldap_public'][$key]['global_search']);
                 }
@@ -470,10 +470,6 @@ public function merge_config()
         }
 
         $this->config = array_merge($this->config, $current);
-
-        foreach (array_keys((array) $current['ldap_public']) as $key) {
-            $this->config['ldap_public'][$key] = $current['ldap_public'][$key];
-        }
     }
 
     /**
diff --git a/tests/Rcmail/Install.php b/tests/Rcmail/Install.php
index fe3ca7cac98..691415104bc 100644
--- a/tests/Rcmail/Install.php
+++ b/tests/Rcmail/Install.php
@@ -116,4 +116,26 @@ function test_list_plugins()
 
         $this->assertSame($acl, $result[0]);
     }
+
+    /**
+     * Test merge_config() method
+     */
+    function test_merge_config()
+    {
+        $config = [
+            'imap_host' => 'ssl://test:993',
+            'smtp_host' => 'ssl://test:465',
+        ];
+
+        $install = rcmail_install::get_instance();
+        $install->configured = true;
+        $install->config = $config;
+
+        $install->merge_config();
+
+        $this->assertSame($config['imap_host'], $install->config['imap_host']);
+        $this->assertSame($config['smtp_host'], $install->config['smtp_host']);
+
+        $this->markTestIncomplete(); // TODO: More tests
+    }
 }