The observer will output a 2 tick signal normally but will output a 1 tick signal when rapidly activated.

Steps to reproduce:

1. Place an observer
2. Place a sticky piston with a block on the output side
3. 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