I use an indoor bike trainer daily. Yesterday was the first day it added steps for me. I'm hoping it was just a fluke, but it sounds as if this is an ongoing problem with your device? I normally bike at a steady pace and gradually increase my speed. Yesterday was also the first time I did intervals on my trainer. That can possibly be what caused it.
There are 125 posts in this thread. Is Garmin doing anything about this calorie/step bug?
My step calories and distance appear believable today; 5300 steps 2.6 mile and 200 odd calories. The only thing I have not done is any formal exercise today. Is it possible it's related?
My data is always okay on days when I only walk and do not have a run. The longer the run, the more the data seems off. On a 6-mile run, sometimes, it's hard to tell. On 17 or more, it's a total mess.
Just now updating to new firmware.
Also, spent 1.5 hours yesterday on phone with Garmin. I zipped up my files and gave it to their engineers. I think they may be working on it. Fingers crossed.