Standard world in survival mode. Around a section of oak and birch trees grown for farming, bamboo shoots appeared, like the middle shoots at numerous altitudes. They broke at random intervals (dropping correctly), and then reappeared a second or two later. Additionally, some of the birch wood blocks transformed into dirt blocks.

I should point out a chunk or two over I have a stand of bamboo growing, but there isn't blocks of dirt at random heights there; the ground is level.

A screenshot of the random bamboo: