MPERF-7015: Session Cookies not stored for shop on root (2nd level) domain

gistfile1.diff

diff --git a/app/code/core/Mage/Core/Model/Session/Abstract.php b/app/code/core/Mage/Core/Model/Session/Abstract.php
index 4d2bf60..c580932 100644
--- a/app/code/core/Mage/Core/Model/Session/Abstract.php
+++ b/app/code/core/Mage/Core/Model/Session/Abstract.php
@@ -566,14 +566,24 @@ public function renewSession()
     {
         $this->getCookie()->delete($this->getSessionName());
         $this->regenerateSessionId();
+        $this->_deleteCookiesForSameParentDomain();
 
+        return $this;
+    }
+
+    /**
+     * Delete Session Cookies For Same Parent Domain
+     *
+     * @return Mage_Core_Model_Session_Abstract
+     */
+    protected function _deleteCookiesForSameParentDomain()
+    {
         $sessionHosts = $this->getSessionHosts();
-        $currentCookieDomain = $this->getCookie()->getDomain();
+        $cookieDomainWithoutLeadDot = ltrim($this->getCookie()->getDomain(), '.');
         if (is_array($sessionHosts)) {
-            foreach (array_keys($sessionHosts) as $host) {
-                // Delete cookies with the same name for parent domains
-                if (strpos($currentCookieDomain, $host) > 0) {
-                    $this->getCookie()->delete($this->getSessionName(), null, $host);
+            foreach (array_keys($sessionHosts) as $sessionHost) {
+                if (strpos($cookieDomainWithoutLeadDot, $sessionHost) > 0) {
+                    $this->getCookie()->delete($this->getSessionName(), null, $sessionHost);
                 }
             }
         }

Hi,
what is the cookie configuration to use with this patch ?
I have http://store.dev (cookie domain: .store.dev) and http://sub.store.dev (cookie domain: .sub.store.dev) with this patch on Magento 1.8.1.0, and i'm still unable to login on sub.store.dev if main store.dev cookie exists.