Not at all sure of why my watch does this but this morning I decided to hit the gym and get some steps in on a treadmill due to rain. Made a HUGE mistake by wearing my running shoes that have a footpod attached. See the following link and you will see why taking my footpod along was a HUGE mistake.
https://connect.garmin.com/modern/activity/1422839513
First, note the average cadence of 131 spm and total time of 54 minutes 57 seconds. Do the math and this should equal 7198 steps. Unfortunately the steps "granted" by the step counter in my 235 was only 5950. BTW, my daily step count goal for today was 16,714 steps so not getting my full measure of steps is rather infuriating.
Second issue was that the stride length was listed at 0.96m when using GPS at this pace on pavement with this footpod the stride length comes in at 0.87 to 0.88m. As a result the treadmill showed a distance of 3.92 miles while my watch showed a distance of 4.26 miles. BTW, if I walk on a treadmill with shoes that do NOT have the footpod mounted the mileage and step count correspond with the reading on the treadmill and my typical step count per mile when using GPS. I'll also note that I am 5 ft. 10 inches so a 0.96 stride length is not sustainable for me for any extended period when walking. Quite simply there is some kind of conflict created by using your footpod with the 235 on a treadmill.
The third issue is based on my experience with the Forerunner 15. With the 15 you can use the heart rate contacts on a treadmill and get a fairly representative step count. Do the same with the 235 and the step count will be some random number between 0 and 50 or 75 steps per mile walked. The same thing will also happen with the 235 if you happen to put your hands in your jacket pocket because it's a cold morning.
The fourth issue is that if you have a footpod present when using an Elliptical Trainer you'll find that the Step Counter doesn't register anything at all. While that statement probably goes against what should happen try it for yourself and you'll see this is true. Because of this I've learned to NOT take a footpod to the gym if I expect to do any work on an Elliptical. Unfortunately for me this morning I was planning on going 100% on the treadmill in attempt to get the maximum potential steps per minute and that didn't happen because the step counter wasn't tracking properly. Truth is that I could have got the same step count using an Elliptical and not beat my tender feet up walking.
Obviously in my opinion the Step Counter in the much less expensive Forerunner 15 is VASTLY superior to the Step Counter in the 235. If this lack of fine sensitivity is something that can be addressed with a future firmware change I would appreciate that being put at the top of the list.