A redstone signal can pass through a piston like how it would be if you powered a block by repeater / redstone torch, but only when the piston is retracting.
This is similar to the bug reported here, except the examples shown there no longer work in 19w02a.
Except I found cases where the bug still works, as shown in the video below.
What I expected to happen was...:
Redstone signal should not have passed through the piston
What actually happened was...:
I could retrieve a redstone signal output from the piston, but only during the piston's retraction.
Steps to Reproduce:
Video shows examples and easy redstone contraptions to reproduce bug.
More examples can be found in ilmango's video: https://www.youtube.com/watch?v=XxMa0O5rAiw
Linked issues
is duplicated by 2
Comments 5
Agreed, will forward-resolve.
Given this is a duplicate of MC-140554, shouldn't this be marked as Confirmed?

Is this still an issue in 19w12b?
Yes it is, see MC-146539
This is actually a duplicate of MC-140554, not related. (Though this ticket describes the bug much better.)