1) A sticky piston is facing up and an observer is placed on top of it (img1). -> Piston is unpowered for 2 redstone ticks.
Observer's behavior is inconsistent when:
    a) the observer's output side is facing up (it gives off signal twice)
    b) oriented any other direction (does nothing)

2) A sticky piston is facing up and a BLOCK is placed on top of it. There is also a noteblock above that BLOCK (img2). -> Piston is unpowered for 2 redstone ticks.
Noteblock's behavior is different if that BLOCK is:
    a) a non instrument-changing block (img2 on the left) -> nothing happens - expected behavior
    b) a instrument-changing block (img2 on the right) -> noteblock changes instrument to harp and then back to that block's instrument and that can be detected with another observer - expected behavior
    c) an observer (a instrument-changing block) (img2 in the middle) -> instrument is changed to harp and never updated even if repeated (unless facing up then it behaves like in b) ) - unexpected behavior