diff -up flag/flag.inc flag_new/flag.inc
--- flag/flag.inc	2008-10-16 18:13:00.000000000 +0200
+++ flag_new/flag.inc	2008-12-30 09:25:44.000000000 +0100
@@ -338,6 +338,7 @@ class flag_flag {
    *   applicable to the item, etc.), TRUE otherwise.
    */
   function flag($action, $content_id, $account = NULL, $skip_permission_check = FALSE) {
+    $sid = session_api_get_sid();
     if (!isset($account)) {
       $account = $GLOBALS['user'];
     }
@@ -345,14 +346,14 @@ class flag_flag {
       return FALSE;
     }
 
-    if (!$account->uid) {
+    /*if (!$account->uid) {
       // Anonymous users can't flag with this system. For now.
       //
       // @todo This is legacy code. $flag->user_access() should handle this.
       // This will also make it posible to have flags that do support anonymous
       // users.
       return FALSE;
-    }
+    }*/
     
     if (!$skip_permission_check && !$this->user_access($account)) {
       // User has no permission to use this flag.
@@ -369,14 +370,15 @@ class flag_flag {
 
     // Perform the flagging or unflagging of this flag.
     $uid = $this->global ? 0 : $account->uid;
-    $flagged = $this->_is_flagged($content_id, $uid);
+    $sid = session_api_get_sid();
+    $flagged = $this->_is_flagged($content_id, $uid, $sid);
     if ($action == 'unflag' && $flagged) {
-      $this->_unflag($content_id, $uid);
+      $this->_unflag($content_id, $uid, $sid);
       // Let other modules perform actions.
       module_invoke_all('flag', 'unflag', $this, $content_id, $account);
     }
     elseif ($action == 'flag' && !$flagged) {
-      $this->_flag($content_id, $uid);
+      $this->_flag($content_id, $uid, $sid);
       // Let other modules perform actions.
       module_invoke_all('flag', 'flag', $this, $content_id, $account);
     }
@@ -394,17 +396,18 @@ class flag_flag {
    *   Optional. The user ID whose flags we're checking. If none given, the
    *   current user will be used.
    */
-  function is_flagged($content_id, $uid = NULL) {
+  function is_flagged($content_id, $uid = NULL, $sid = NULL) {
     $uid = !isset($uid) ? $GLOBALS['user']->uid : $uid;
+    $sid = !isset($sid) ? session_api_get_sid() : $sid;
 
     // flag_get_user_flags() alreday does caching, but nevertheless we manage a
     // cache of our own to save on function calls.
     static $flag_status = array();
-    if (!isset($flag_status[$uid][$this->content_type][$content_id])) {
-      $flag_status[$uid][$this->content_type][$content_id] = flag_get_user_flags($this->content_type, $content_id, $uid);
+    if (!isset($flag_status[$sid][$this->content_type][$content_id])) { # Array CAMBIATO
+      $flag_status[$sid][$this->content_type][$content_id] = flag_get_user_flags($this->content_type, $content_id, $uid, $sid);
     }
 
-    return isset($flag_status[$uid][$this->content_type][$content_id][$this->name]);
+    return isset($flag_status[$sid][$this->content_type][$content_id][$this->name]);
   }
 
   /**
@@ -419,8 +422,8 @@ class flag_flag {
    *
    * @private
    */
-  function _is_flagged($content_id, $uid) {
-    return db_result(db_query("SELECT fid FROM {flag_content} WHERE fid = %d AND uid = %d AND content_id = %d", $this->fid, $uid, $content_id));
+  function _is_flagged($content_id, $uid, $sid) {
+    return db_result(db_query("SELECT fid FROM {flag_content} WHERE fid = %d AND uid = %d AND sid = %d AND content_id = %d", $this->fid, $uid, session_api_get_sid(), $content_id));
   }
 
   /**
@@ -431,8 +434,8 @@ class flag_flag {
    *
    * @private
    */
-  function _flag($content_id, $uid) {
-    db_query("INSERT INTO {flag_content} (fid, content_type, content_id, uid, timestamp) VALUES (%d, '%s', %d, %d, %d)", $this->fid, $this->content_type, $content_id, $uid, time());
+  function _flag($content_id, $uid, $sid) {
+    db_query("INSERT INTO {flag_content} (fid, content_type, content_id, uid, sid, timestamp) VALUES (%d, '%s', %d, %d, %d, %d)", $this->fid, $this->content_type, $content_id, $uid, $sid, time());
     $this->_update_count($content_id);
   }
 
@@ -444,8 +447,8 @@ class flag_flag {
    *
    * @private
    */
-  function _unflag($content_id, $uid) {
-    db_query("DELETE FROM {flag_content} WHERE fid = %d AND uid = %d AND content_id = %d", $this->fid, $uid, $content_id);
+  function _unflag($content_id, $uid, $sid) {
+    db_query("DELETE FROM {flag_content} WHERE fid = %d AND uid = %d AND sid = %d AND content_id = %d", $this->fid, $uid, $sid, $content_id);
     $this->_update_count($content_id);
   }
 
@@ -478,8 +481,8 @@ class flag_flag {
    *
    * For global flags, pass '0' as the user ID.
    */
-  function get_user_count($uid) {
-    return db_result(db_query('SELECT COUNT(*) FROM {flag_content} WHERE fid = %d AND uid = %d', $this->fid, $uid));
+  function get_user_count($uid, $sid) {
+    return db_result(db_query('SELECT COUNT(*) FROM {flag_content} WHERE fid = %d AND uid = %d AND sid = %d', $this->fid, $uid, session_api_get_sid()));
   }
 
   /**
diff -up flag/flag.install flag_new/flag.install
--- flag/flag.install	2008-10-22 23:50:20.000000000 +0200
+++ flag_new/flag.install	2008-12-29 14:47:35.000000000 +0100
@@ -174,6 +174,12 @@ function flag_schema() {
         'not null' => TRUE,
         'default' => 0,
       ),
+      'sid' => array(
+        'type' => 'int',
+        'unsigned' => TRUE,
+        'not null' => TRUE,
+        'default' => 0,
+      ),
       'timestamp' => array(
         'type' => 'int',
         'unsigned' => TRUE,
@@ -182,10 +188,11 @@ function flag_schema() {
         'disp-size' => 11,
       )
     ),
-    'primary key' => array('fid', 'content_type', 'content_id', 'uid'),
+    # 'primary key' => array('fid', 'content_type', 'content_id', 'uid'),
+    'primary key' => array('fid', 'content_type', 'content_id', 'uid', 'sid'),
     'indexes' => array(
       'content_type_content_id' => array('content_type', 'content_id'),
-      'content_type_uid' => array('content_type', 'uid'),
+      'content_type_uid' => array('content_type', 'uid', 'sid'),
     ),
   );
 
diff -up flag/flag.module flag_new/flag.module
--- flag/flag.module	2008-10-13 13:29:01.000000000 +0200
+++ flag_new/flag.module	2008-12-29 15:54:16.000000000 +0100
@@ -132,9 +132,9 @@ function flag_link($type, $object = NULL
   global $user;
 
   // Anonymous users can't create flags with this system.
-  if (!$user->uid) {
+  /*if (!$user->uid) {
     return;
-  }
+  }*/
 
   // Get all possible flags for this content-type.
   $flags = flag_get_flags($type);
@@ -200,9 +200,9 @@ function flag_form_alter(&$form, &$form_
   }
   elseif (isset($form['type']) && isset($form['#node'])
       && ($form_id == $form['type']['#value'] .'_node_form')) {
-    if (!$user->uid) {
+    /*if (!$user->uid) {
       return;
-    }
+    }*/
 
     $nid = !empty($form['nid']['#value']) ? $form['nid']['#value'] : NULL;
 
@@ -277,7 +277,7 @@ function flag_user($op, &$edit, &$accoun
   switch ($op) {
     case 'delete':
       // Remove flags by this user.
-      db_query("DELETE FROM {flag_content} WHERE uid = %d", $account->uid);
+      db_query("DELETE FROM {flag_content} WHERE uid = %d AND sid = %d", $account->uid, session_api_get_sid());
       break;
     case 'view';
       $flags = flag_get_flags('user');
@@ -535,7 +535,8 @@ function flag_form(&$form_state, $name, 
   $form['roles'] = array(
     '#type' => 'checkboxes',
     '#title' => t('Roles that may use this flag'),
-    '#options' => user_roles(TRUE),
+    #'#options' => user_roles(TRUE),
+    '#options' => user_roles(), # cfr. http://drupal.org/node/271582#comment-885356
     '#default_value' => $flag->roles,
     '#required' => TRUE,
     '#description' => t('Checking <em>authenticated user</em> will allow all logged-in users to flag content with this flag. Anonymous users may not flag content.'),
@@ -1038,33 +1039,34 @@ function flag_get_flags($content_type = 
  *   [nid] => [name] => Object from above.
  *
  */
-function flag_get_user_flags($content_type, $content_id = NULL, $uid = NULL, $reset = FALSE) {
+function flag_get_user_flags($content_type, $content_id = NULL, $uid = NULL, $sid = NULL, $reset = FALSE) {
   static $flagged_content;
 
   $uid = !isset($uid) ? $GLOBALS['user']->uid : $uid;
+  $sid = !isset($sid) ? session_api_get_sid() : $sid;
 
   if (isset($content_id)) {
-    if (!isset($flagged_content[$uid][$content_type][$content_id]) || $reset) {
+    if (!isset($flagged_content[$sid][$content_type][$content_id]) || $reset) {
       $flags = flag_get_flags($content_type);
-      $flagged_content[$uid][$content_type][$content_id] = array();
-      $result = db_query("SELECT * FROM {flag_content} WHERE content_type = '%s' AND content_id = %d AND (uid = %d OR uid = 0)", $content_type, $content_id, $uid);
+      $flagged_content[$sid][$content_type][$content_id] = array();
+      $result = db_query("SELECT * FROM {flag_content} WHERE content_type = '%s' AND content_id = %d AND (uid = %d OR uid = 0) AND sid = %s", $content_type, $content_id, $uid, $sid);
       while ($flag = db_fetch_object($result)) {
-        $flagged_content[$uid][$content_type][$content_id][$flags[$flag->fid]->name] = $flag;
+        $flagged_content[$sid][$content_type][$content_id][$flags[$flag->fid]->name] = $flag;
       }
     }
-    return $flagged_content[$uid][$content_type][$content_id];
+    return $flagged_content[$sid][$content_type][$content_id];
   }
 
   else {
-    if (!isset($flagged_content[$uid]['all'][$content_type]) || $reset) {
+    if (!isset($flagged_content[$sid]['all'][$content_type]) || $reset) {
       $flags = flag_get_flags($content_type);
-      $flagged_content[$uid]['all'][$content_type] = TRUE;
-      $result = db_query("SELECT * FROM {flag_content} WHERE content_type = '%s' AND (uid = %d OR uid = 0)", $content_type, $uid);
+      $flagged_content[$sid]['all'][$content_type] = TRUE;
+      $result = db_query("SELECT * FROM {flag_content} WHERE content_type = '%s' AND (uid = %d OR uid = 0) AND sid = %s", $content_type, $uid, $sid);
       while ($flag = db_fetch_object($result)) {
-        $flagged_content[$uid][$content_type]['all'][$flags[$flag->fid]->name][$flag->content_id] = $flag;
+        $flagged_content[$sid][$content_type]['all'][$flags[$flag->fid]->name][$flag->content_id] = $flag;
       }
     }
-    return $flagged_content[$uid][$content_type]['all'];
+    return $flagged_content[$sid][$content_type]['all'];
   }
 
 }
Common subdirectories: flag/includes and flag_new/includes
Common subdirectories: flag/theme and flag_new/theme
Common subdirectories: flag/translations and flag_new/translations