Make something like this (look in attachment) and you will wonder the the piston move 1 times but doesnt retrackt, it only retrackt when you place/break a block next to it and when you break the redstone.
and i excepted that the piston goes back, now my redstone machine is broken 
- duplicates
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MC-11193 The order in which powerable blocks (e.g. redstone dust blocks) along a wire are powered or de-powered is not clearly defined and causes a non-deterministic behavior for redstone contraptions
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