Saving custom permalink structure forcing "/index.php/%postname%/"

Hello 🙂

I have a WP network using a ‘/%postname%/’ custom permalink structure – which works just fine, however if i press ‘Save Changes’ on the Settings->Permalinks admin page, it will force the custom structure to be ‘/index.php/%postname%/’.

This is having several negative knock-on effects, {for example passing data via a query string to a form}, how can i prevent this?

I’m running WP 3.2.1 on a dedicated server running Windows Server 2003 and IIS 6.

Thanks in advance,

AB24