When I connect a piece of redstone to another in a corner pattern, as shown in the screenshots, there is a graphical glitch depending on what way the redstone corner is facing.
How to replicate: R=Redstone
R R R
R ---R
R R R
This should give you the glitch.
Environment
Mac OSX 10.9 Java 1.6.0_65 64 bit
Dupe MC-66970