Pistons behave like half slabs/transparent blocks regarding redstone, this means that redstone dust stays connected even if it is "blocked" by a piston.
If redstone dust is powered from below a piston, then travels up to one block next to the piston nothing happens. If it travels another block, the piston extends. See the attached screenshots for details.
I expected the piston to react the same in both situations, either extend or retract.
This is a duplicate of MC-80848, but since that was wrongly closed, and bug reports unfortunately have a very small chance to get re-opened, I created this one.
Related issues
Attachments
Comments


Still WAI. Still a dupe of MC-108

In what way is this a dupe of MC-108? There is literally no quasi-connectivity going on here at all.

The redstone dust that is two blocks away from the piston is powering the piston.

Can you recreate that without the other redstone dust?

This has nothing to do with QC
You can replace the 'other dust' with anything that redirects dust
button, lever, repeater, observer, redstone, comparator, torch etc
its due to how blocks test to see if the dust is pointing towards it
rather than testing if the dust is pointing towards it
it tests if the dust is pointing away from it AND is NOT pointing to the left OR right