When certain things happen like block updates, some numbers on the status bar flicker.
Steps to reproduce:
Create a redstone circuit with repeaters.
Supply power to it
Notice that when a repeater is powered, a number on the status bar flickers
Environment
Minecraft Version: 1.5.1
Operating System: Windows 8 (amd64) version 6.2
Java Version: 1.7.0_09, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Duplicate of MC-11033.