That's just the width in pixels of your display, at 960px it will go down into mobile mode as it's a responsive design, but it's still the same skin. It's odd your tablet should be that narrow tbh as my 8 inch tab renders in desktop mode, and I know that even the nexus 7 renders ok in desktop mode too. Don't know if there's a setting somewhere which is perhaps doubling up on pixels, as if it's an hd tablet it's going to have more than 960px width available to it?