In most of the dances, there is a school of thought that the foot goes in the direction of travel, while the body rotates or opens as necessary to get out of the partner's way. This is the form of CBM usually practiced by Eggleton-inspired dancers.
But there is another school of thought where the body and feet remain more aligned, and thus would both open somewhat on a curved track to accomodate the partner. This style is commonly associated with the students of Bill Irvine. It's worth noting though that the actual differences are fairly subtle, compared to the grossly overdone distortions of each method common in the wild.
But where it gets really interesting is that I know of at least one Eggleton style teacher who claims that viennese waltz doesn't really have CBM... finally we figured out that what they mean is that they dance VW with something more like an Irvine style body and foot CBM, which doesn't really feel like CBM to an Eggleton style dancer used to associating a feeling of internal twist with CBM.