If a power source block is placed above a piston/ sticky piston with one block space between them, and the piston is updated via placing a block next to it, it will extend and will remain extended even if the power source is removed. The piston will then only retract if it is updated again.
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LyghtningWither
This is called quasi-connectivity, something that started out as a bug, but is basically now a feature in Java Edition. You can read more about it on the Minecraft Wiki: https://minecraft.gamepedia.com/Tutorials/Quasi-connectivity