Step to reproduce
1. /setblock x y z piston_extension on your world.
2. Press F3 to see before and after.
3. You can see chunk updates every time and ram is running faster.
Video : https://www.youtube.com/watch?v=dysIrNyNqfA
Also, you can see the force crash report.
Environment
OS : Windows 7 Ultimate (x86) 6.1 Service Pack 1
CPU : Pentium(R) Dual-Core CPU E5400 @ 2.70GHz
RAM : 2 GB DDR-2 RAM
Java : Java Development Kit 1.7.0 Update 75 (Used for modding)
Graphic Card : NVIDIA GeForce 9500 GT
OpenGL Version : 3.3
Unfixable. MC-66341