I made this "death machine" a long time ago, and I thought it got fixed but when I tried it again, it still occurs. It seems that it accumulates fall damage of a hearts or so and can kill someone. The max damage that occurred for me was 3.5 hearts.

YouTube Video: http://youtu.be/F1JlYjJU8j0
It didn't really occur well in the video. When I wasn't recording the machine was more effective (happening more often and more damage)

Steps To Reproduce:
Remake the machine I set up in the picture. (all one layer)
Then give it a 1 tick pulse. (place a redstone torch on the redstone block)
Stand between the 4 pistons
After a few moments you will randomly take fall damage (indicated by the falling particles)