This is the first (and only) time, I could get this bug to work. (I can not recreate it)
While on a clock, the piston pushes the observer back and forth and in some strange way becomes the redstone powered.
MC-169073
Observer activating redstone 1 block away
Resolved
Duplicate
0
This is a duplicate of MC-160258. The only reason this may look strange is because the repeater is on such a long delay. Because repeaters are visually only powered when outputting a signal, it takes the repeater several ticks to display the pulse from the observer.