Block duplication using pistons and slime blocks

Using the setup below the diamond block connected to the slime block seems to be occasionally duplicated. The blocks may actually be Block 36, and remains in world upon quitting and reloading in Single Player.

Setup used:
http://s2.postimg.org/5pyr2obq1/2015_03_05_21_12_25.png

clock ----> pulse shortener ----> delay manager ----> piston & slime block