If you put 4 regular rails down in a T shape, and you put a redstone torch or redstone block next to the junction, it doesn't switch. On the other hand, placing a lever replacing the torch and powering the lever will activate the junction.
Here is a list of other things that work:
Pressure plates
Buttons
Levers
Tripwires
Redstone
Redstone Chests
Detector rails
Repeaters
Comparators
This is because all these things are placed unpowered, but redstone torches and redstone blocks are placed powered.
See Etho's LP Video: https://www.youtube.com/watch?v=Vfi8czqZo_0
7min 5sec
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Please test in 1.9-pre4.

Dupe of MC-11142