mcMMO-Dev/mcMMO — pull request #544 by Glitchfinder (2013-01-21 02:08:57+00:00)
Title: Fixing a new duping bug. And this time it was NOT our fault!

A change in vanilla minecraft was to blame. They changed how blocks are affected when pistons retract, and it takes something like three ticks for all of the block changes to finish up now.