I have just experienced this and it seems to have only just started in the past few days. If I log in to my admin panel it seems to get confused and starts implanting the main site within the admin dashboard and if I refresh the page the redirect keeps happening.
I have tried all the obvious to fix it to!
renamed the plugins folder
renamed the theme to use a standard one
complete fresh install
I have kind of tracked it down to the wordpress cookies as the cause of it!
