When i created a new world, i walked to east direction, i found this, and i waited for 3 minutes and nothing happen (around 4 chunks affected)...
Environment
Windows 7 32 bits, Intel Celeron Dual Core @ 1.60 GHz, Java version 7 update 71, Graphic Card: NVIDIA GT520 1G DDR3 2G DDR3, drivers version 344.75...
Don't duplicate your own tickets.