nav widget displaying differently between preview and live

Not sure how to fully describe this, but the basic thing is...

We've just "activated" the Mobile Module in Sitefinity version 6, to manage Responsive design.

I want the site's main menu to change on tablets and smartphones.

The site is an upgrade from Sitefinity version 3.

I can see that the "old" navigation widget refuses to interact with the module, so I've dragged and dropped a brand new navigation widget into the homepage's template file.

If I preview my homepage from within Sitefinity's Admin area, I can see the menu changed - reflecting how I've set-up the rules within the module.

But, if I then view the site from the front-end, the homepage displays the "standard" desktop format of the menu, be it on desktop, tablet or smartphone.

I'm baffled as to why the internal preview is "correct" but by browsing the site's URL directly and it's "wrong". It's a clone of the live website, running on the same server off of a subdomain of the live site.

Any thoughts greatfully received.

m.