(Sticky) Pistons fail to retract under certain circumstances:
A piston pushing a redstone block up will not retract after redstone power is removed, even if a block is placed next to the piston to update it.
[media]It's worth noting that all other directions have no trouble retracting.
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In addition, the following redstone configuration results in the same problem, no matter the piston's direction. After placing the wool, however, the piston does update.
[media](Sorry if this is a duplicate of 108, but I couldn't find anything for pistons remaining after being unpowered.)
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Duplicate of MC-108

I believe this is a different issue-- at least for part 1. As the attached images show, this "feature" only occurs with upwards-facing pistons, which leads me to believe this is a bug. In addition, this case differs from MC-108 because placing a block will not update the piston. Instead, the only option is to break the redstone block or the piston itself.
[media][media][media]
The piston is being powered by the redstone block. This is MC-108.