Just simply put redstone wires in an "L" and textures break.
In the screenshot, the wires are put in the spots in the same configuration as the red wool.
MC-67064
Messed up corner redstone wire textures!
Resolved
Duplicate
0
Aidan McCracken
(Unassigned)
Unconfirmed
Minecraft 14w33a
Retrieved
This issue has been reported already. It has been linked to the original bugreport.
Please search before reporting any bugs, as it's likely that one exists already.