I also use the trusty Zephyr HxM and my steps seem reasonable. I checked by jogging for 1min up and down my street and counted my steps, about 120spm because I'm old and lazy :-).
I noticed when I exported a TCX file to another program the cadence doubled because it thought I was cycling. Cycling triggers each revolution of crank from magnet only on one pedal, left foot and right foot for 1 revolution trigger = half of running triggers (bump for left foot, bump for right foot) from the HxM accelerometer.
Steps per min = 2x revolutions per min.
I do own my HxM a long time now... and had to change my running app this year..
Had before SportsTrackLive (the old paid version)
Now my cadence speeds (steps per minute) are unreasonable high - I had around 70 with STL and now around 140 with run.gps ... why?
Speed is configured for GPS - on my old trusty LG Google Nexus 5 (32GB + Android 10) and was perfectly working with STL before - and speed and distance records are also OK!
What can I do?
Also sorry for digging out such old thread..
I'am trying to calibrate with my own little software I made.
I might need beta tester by the way, if I'am able to finish before the end of my holidays.
see my other thread:
http://www.gps-sport.net/forums/thread/1211-0/HxM-distance-and-speed-accuracy-disappointing-