The bug
The timing of a comparator in subtraction mode is affected by an appropriately synchronized redstone wire placed on the other side of a one wide gap (see attached screenshot).
On a rising edge generated at (1), the delay between (2) turning off and (3) turning on is 1 redstone tick if the piece of redstone wire marked in purple does not exist, and it is 0 ticks if it exists. The direction of the redstone wire does not matter as long as it is connected appropriately.
The behavior in case of a falling edge at (1) seems to be unaffected.
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Comments 5
Is this still a issue in the latest version of the game(currently 1.13.1)?
If so, please add it to the affected versions, thanks!
Confirmed Not been fixed for 1.14
The bug is caused by MC-12211 which has a possible fix in the comments
The reason why this happens is very specific and hard to track down (in game)
I've known people that have built whole computers in MC with redstone, only to scrape it because this bug is causing major unknown timing issues
How it works/to reproduce
Put a comparator in subtract mode and place it in the 'bugged on state' via powering the back input and then the side input with the same signal strength.
Increase the signal strength of the back input or decrease the side.
Give the comparator a block update (via redstone, repeater, comparator, torch etc) 2gt (1redstone tick) before depowering the side input (unlocking)
If you set up a timing circuit to test the delay of the comparator, you will notice that its instant
If the comparator is not in the 'bugged on state', back input signal strength smaller than the sides or given a block update 2gt before being unlocked, the comparator will not be instant.
Confirmed for 15w51b... very strange
Doesn't seem to depend on orientation.