I don't believe that the act of placing one foot in line with the other would naturally result in CBMP, not from a standing square, feet together, starting point anyway.
Here's some food for thought:
If you stand with your feet together and step absolutely straight forward, the feet are on two separate, albeit narrowly spaced tracks. Therefore to place one foot along or across the track of the other is to shift sideways, even if only very slightly.
Now you might think that you're facing squarely to the direction you are stepping, but that's not actually true. If you face LOD and step foward with your left foot in CBMP, your movement is almost, but not quite, down LOD. It's actually on just a slight diagonal towards the wall. Now although you're facing squarely to the LOD, with respect to the direction you're traveling, you're not quite square. You do in fact have your right side just slightly in front of your left.
So one could indeed reasonably argue that any step taken with one foot along the track of the other is in CBMP, even when the body and feet are perfectly in line with each other.
Jonathan