I found this problem too. If kneels down and bring you down again, you can hear the sound of footsteps as if you were walking.
To reproduce it:
1. put a soldier by editor and hit preview to control your soldier
2. hit "X" on keyboard to kneel
3. hit "CTRL+S" on keyoard to kneel down a bit
Now don't move and you will hear the footsteps.
The sound reproduced depends on the underlying soil.