I base my assumption on the 235 using a single axis step counter on one simple fact that can clearly be demonstrated by just swinging your arm at a standstill. On the 235 doing this will result in steps being counted as long as you swing your arm more than 10 times. Try the same on the older Forerunner 15 and you'll see almost ZERO steps recorded. I've also seen many occasions when putting my hands in my pocket while walking the dog will result in very few steps being recorded on the 235. Sum it all up and the step counter in the 235 is poor in comparison to that in the older model 15.
Additionally, I think the screen only updates once per minute. That's also why you won't see the steps update while you are stepping. :-)