It's not just when a unit falls into a wall, it's when any unit dies near a wall created using CreateVehicle.

It has to do with the dev build, getting this rpt:

Error: Failed to open file a3\sounds_f\characters\footsteps\dirt_run_new_4.wav
Cannot load sound 'a3\sounds_f\characters\footsteps\dirt_run_new_4.wav'
Error: Failed to open file a3\sounds_f\characters\footsteps\dirt_run_new_1.wav
Cannot load sound 'a3\sounds_f\characters\footsteps\dirt_run_new_1.wav'
Error: Failed to open file a3\sounds_f\characters\footsteps\dirt_run_new_4.wav
Cannot load sound 'a3\sounds_f\characters\footsteps\dirt_run_new_4.wav'
Error: Failed to open file a3\sounds_f\characters\footsteps\dirt_run_new_1.wav
Cannot load sound 'a3\sounds_f\characters\footsteps\dirt_run_new_1.wav'
Error: Failed to open file a3\sounds_f\characters\footsteps\dirt_run_new_4.wav
Cannot load sound 'a3\sounds_f\characters\footsteps\dirt_run_new_4.wav'
Error: Failed to open file a3\sounds_f\characters\footsteps\dirt_run_new_1.wav
Cannot load sound 'a3\sounds_f\characters\footsteps\dirt_run_new_1.wav'
Error: Failed to open file a3\sounds_f\characters\footsteps\dirt_run_new_4.wav

and so on, and so on