The Bug
Powered buttons do not emit redstone particles when pressed, unlike powered levers, which do.
Steps to Reproduce
Place down a lever and activate it.
Take note of how redstone particles are produced from the powered lever.
Place down a button and activate it.
Take note as to whether or not buttons produce redstone particles when being powered.
Observed Behavior
Buttons don't produce redstone particles when being powered.
Expected Behavior
Buttons would produce redstone particles when being powered.
That is intentional, as you can easily tell if a button is powered. If a lever was placed on the ground, and you placed another lever on the ground next to it then powered it, you wouldn't be able to tell which lever is powered without the particles. A pressed button is clearly visible (due to being half the size), but a lever is not without redstone particles.