If a redstone is placed above the piston and a signal is played to the redstone, the redstone will break and the piston will remain activated even though the redstone signal is not flowing, as shown in the image. (Breaking the redstone block on top does not change the state of the piston.) Then, if you place some block in close contact with the piston, the piston will return.
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Thank you for your report!
We are tracking this issue in MC-108, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as Works As Intended, which means this is not considered a bug and will not be fixed. Please do not leave a comment on the linked ticket.
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google “quasi-connectivity”