Happened to me yesterday on Pre-Release 1 & 2 with Diamond Block, Cobblestone and Granite yesterday. This bug seems related to every block pushed by a Sticky Piston no matter how much Redstone tick pulse. I built another Iron Farm on my mew world and the farm keep resetting over and over because of this bug. So I loaded my new World in 1.8.9 and my farm is working like a charm without these duplicated blocks.
Happened to me yesterday on Pre-Release 1 & 2 with Diamond Block, Cobblestone and Granite yesterday. This bug seems related to every block pushed by a Sticky Piston no matter how much Redstone tick pulse. I built another Iron Farm on my mew world and the farm keep resetting over and over because of this bug. So I loaded my new World in 1.8.9 and my farm is working like a charm without these duplicated blocks.