Using the picture provided, when redstone is placed on/removed from the green wool, it causes the piston to update, even though no block touching the piston was updated.
Edit: The update persists even when the yellow wool is air.
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WAI. See MC-108
addgame
Redstone updates occur two blocks around any redstone related item turned on, placed, or broken unlike block updates which only occur adjacently. It has been like this for a while and it doesn't seem like it will be changed anytime soon.
Torabi
Nothing new about it. Tried the exact same setup in 1.7.9, minus the slime block. Placing redstone updates the piston. Same in 1.6.2.