Dealing with Joomla 1.5 index.php breaking user sessions – This issue occurs mostly with Joomla 1.5
The problem occurs when using the user login module/menu item to redirect a page. By default index.php becomes the default, so even if you leave the fields blank you will generally still see http://www.example.com/index.php instead of http://www.example.com/
This tends to break the session thus the stability of your view of the website, usually a white screen of death scenario or token invalid results, frustrating users who usually threaten to abandon using the offending website. The way around this is to add a meaningful redirect into the fields of the previously mentioned extensions or just add a forward slash (/), no brackets of course.