Every since an upgrade to WordPress 3.3 URLs are not redirecting as they should.
Changed: domain.com/2010/10/postname/ to: domain.com/postname/
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^/[0-9]{4}/[0-9]{2}/(.+)$ /$1 [NC,R=301,L]
The problem was due to the leading slash and not using $3