Domain redirect creates a doubled address

For example let's say you have a domain name www.example.com and you create a redirect for the naked domain example.com to www.example.com. For me I do this using cPanel's GUI for Redirects.

Is there any known reason why occasionally browsers would do the following after entering www.example.com into the address bar:

www.example.com/www.example.com

When this happens it is also cached by the browser, so whenever I go to www.example.com or example.com it will always redirect to www.example.com/www.example.com.