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.