How to reproduce:
1.- Take a piston, both sticky and normal works.
2.- Power it, eg. a lever.
3.- Un power it.

What is supposed to happen?
Nothing, just the piston retracting.

What happens?
When the piston is fully retracted it becomes invisible for a second.

Video:
http://youtu.be/ubrtPgzwRPo

Pictures:
http://prntscr.com/814x4j Invisible piston.
http://prntscr.com/814x8w The piston is there