diff --git a/src/includes/class/class.LSsearch.php b/src/includes/class/class.LSsearch.php
index 9b306608..b1a3df87 100644
--- a/src/includes/class/class.LSsearch.php
+++ b/src/includes/class/class.LSsearch.php
@@ -156,7 +156,7 @@ class LSsearch extends LSlog_staticLoggerClass {
       }
     }
     else {
-      $this -> purgeParams($LSobject);
+      $this -> purgeParams($LSobject, $context);
       $this -> loadDefaultParameters();
     }
 
@@ -214,7 +214,14 @@ class LSsearch extends LSlog_staticLoggerClass {
    * @return boolean True if params has been loaded from session or False
    */
   private function loadParamsFromSession() {
-    if (isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context]) && is_array($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context])) {
+    if (
+      isset($_SESSION['LSsession'])
+      && isset($_SESSION['LSsession']['LSsearch'])
+      && isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject])
+      && isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'])
+      && isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context])
+      && is_array($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context])
+    ) {
       self :: log_debug('Load params from session for context '.$this -> context);
       $params = $_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context];
 
@@ -236,15 +243,28 @@ class LSsearch extends LSlog_staticLoggerClass {
    * @return void
    */
   private function saveParamsInSession() {
-    self :: log_debug('Save context params session '.$this -> context);
+    self :: log_debug(
+      'saveParamsInSession(".$this -> LSobject."): Save context params session '.$this -> context);
     $params = $this -> params;
     if ($params['filter'] instanceof Net_LDAP2_Filter) {
       $params['filter'] = $params['filter'] -> asString();
     }
-
+    if (!isset($_SESSION['LSsession']))
+      $_SESSION['LSsession'] = array();
+    if (!isset($_SESSION['LSsession']['LSsearch']))
+      $_SESSION['LSsession']['LSsearch'] = array();
+    if (!isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]))
+      $_SESSION['LSsession']['LSsearch'][$this -> LSobject] = array();
+    if (!isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params']))
+      $_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'] = array();
+    if (!isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context]))
+      $_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context] = array();
     foreach ($params as $param => $value) {
-      if ( !isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context][$param]) || $_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context][$param]!=$value) {
-        self :: log_trace("$param => ".varDump($value));
+      if (
+        !isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context][$param])
+        || $_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context][$param] != $value
+      ) {
+        self :: log_trace("saveParamsInSession(".$this -> LSobject."): $param => ".varDump($value));
         $_SESSION['LSsession']['LSsearch'][$this -> LSobject]['params'][$this -> context][$param]=$value;
       }
     }
@@ -253,30 +273,61 @@ class LSsearch extends LSlog_staticLoggerClass {
   /**
    * Purge parameters in session
    *
-   * @param string $LSobject The LSobject type
+   * @param string $LSobject The LdapObject type
+   * @param string|null $context The context of the search (optional, default: null)
    *
    * @return void
    */
-  public static function purgeParams($LSobject) {
-    unset($_SESSION['LSsession']['LSsearch'][$LSobject]['params']);
+  public static function purgeParams($LSobject, $context=null) {
+    if (!isset($_SESSION['LSsession'])) return;
+    if (!isset($_SESSION['LSsession']['LSsearch'])) return;
+    if (!isset($_SESSION['LSsession']['LSsearch'][$LSobject])) return;
+    if (!isset($_SESSION['LSsession']['LSsearch'][$LSobject]['params'])) return;
+    if ($context) {
+      if (isset($_SESSION['LSsession']['LSsearch'][$LSobject]['params'][$context]))
+        unset($_SESSION['LSsession']['LSsearch'][$LSobject]['params'][$context]);
+    }
+    else
+      unset($_SESSION['LSsession']['LSsearch'][$LSobject]['params']);
   }
 
   /**
    * Purge cache
    *
+   * @param string $LSobject The LdapObject type
+   * @param string|null $hash The hash of the search (optional, default: null)
+   *
    * @return void
    */
-  public static function purgeCache($LSobject) {
-    unset($_SESSION['LSsession']['LSsearch'][$LSobject]);
+  public static function purgeCache($LSobject, $hash=null) {
+    if (!isset($_SESSION['LSsession'])) return;
+    if (!isset($_SESSION['LSsession']['LSsearch'])) return;
+    if (!isset($_SESSION['LSsession']['LSsearch'][$LSobject])) return;
+    if (!isset($_SESSION['LSsession']['LSsearch'][$LSobject]['cache'])) return;
+    if ($hash) {
+      if (isset($_SESSION['LSsession']['LSsearch'][$LSobject]['cache'][$hash]))
+        unset($_SESSION['LSsession']['LSsearch'][$LSobject]['cache'][$hash]);
+    }
+    else
+      unset($_SESSION['LSsession']['LSsearch'][$LSobject]['cache']);
   }
 
   /**
    * Purge session
    *
+   * @param string $LSobject The LdapObject type
+   *
    * @return void
    */
-  private function purgeSession() {
-    unset($_SESSION['LSsession']['LSsearch']);
+  private function purgeSession($LSobject=null) {
+    if (!isset($_SESSION['LSsession'])) return;
+    if (!isset($_SESSION['LSsession']['LSsearch'])) return;
+    if ($LSobject) {
+      if (isset($_SESSION['LSsession']['LSsearch'][$LSobject]))
+        unset($_SESSION['LSsession']['LSsearch'][$LSobject]);
+    }
+    else
+      unset($_SESSION['LSsession']['LSsearch']);
   }
 
   /**
@@ -1121,7 +1172,15 @@ class LSsearch extends LSlog_staticLoggerClass {
     if ($this -> cacheIsEnabled()) {
       $hash = $this->getHash();
       self :: log_trace("addResultToCache(): Save result in cache with hash '$hash'.");
-      $_SESSION['LSsession']['LSsearch'][$this -> LSobject][$hash]=$this->result;
+      if (!isset($_SESSION['LSsession']))
+        $_SESSION['LSsession'] = array();
+      if (!isset($_SESSION['LSsession']['LSsearch']))
+        $_SESSION['LSsession']['LSsearch'] = array();
+      if (!isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]))
+        $_SESSION['LSsession']['LSsearch'][$this -> LSobject] = array();
+      if (!isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['cache']))
+        $_SESSION['LSsession']['LSsearch'][$this -> LSobject]['cache'] = array();
+      $_SESSION['LSsession']['LSsearch'][$this -> LSobject]['cache'][$hash] = $this->result;
     }
     else
       self :: log_trace('addResultToCache(): cache is disabled.');
@@ -1134,10 +1193,16 @@ class LSsearch extends LSlog_staticLoggerClass {
    **/
   private function getResultFromCache() {
     if ($this -> cacheIsEnabled()) {
-      $hash=$this->getHash();
-      if (isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject][$hash])) {
+      $hash = $this->getHash();
+      if (
+        isset($_SESSION['LSsession'])
+        && isset($_SESSION['LSsession']['LSsearch'])
+        && isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject])
+        && isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['cache'])
+        && isset($_SESSION['LSsession']['LSsearch'][$this -> LSobject]['cache'][$hash])
+      ) {
         self :: log_trace('getResultFromCache(): result found in cache.');
-        return $_SESSION['LSsession']['LSsearch'][$this -> LSobject][$hash];
+        return $_SESSION['LSsession']['LSsearch'][$this -> LSobject]['cache'][$hash];
       }
       self :: log_trace('getResultFromCache(): result not found in cache.');
     }