I have recently encountered a weird piston behavior, where either a normal piston or a sticky one can be powered from the distance of two blocks. This is only possible by using redstone blocks (as far as I know).
Steps to reproduce:
place down a sticky/normal piston facing any way,
grab two redstone blocks and place them on top of the piston,
destroy the middle block and that's it
Note: This would also work if your middle block wasn't a redstone block. I have recorded a video to make it easier for you to visualize. I have also tested it on 1.8 and 1.10 (I was able to reproduce it). And make sure your piston receives a block update.
Video: https://www.youtube.com/watch?v=tor1CBQcyb0&feature=youtu.be
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violine1101
Thank you for your report!
We're actually already tracking this issue in MC-108, so I resolved and linked this ticket as a duplicate.
However, that ticket has already been resolved. Depending on the resolution, that can mean that it either will be fixed in the next version, or that it is not considered a bug and won't be fixed.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
As far as I know this is not a bug, this is just quasi connectivity.