The observer will output a 2 tick signal normally but will output a 1 tick signal when rapidly activated.
Steps to reproduce:
Place an observer
Place a sticky piston with a block on the output side
Place a repeater in front of the observer and hold down
Gif of bug: https://gfycat.com/PoshMistyAmericancrocodile
Gif was posted by a moderator NOT me
you can reproduce put a repeater in front of the observers detection side and hold down place block on the repeater to change the state the observer will start with a 2 tick pulse and after that to 1 tick pulses