Using the setblock command to replace a button creates multiple possible problems.

How to recreate:

1) Press a button

2) Before the button becomes unpowered, use setblock to replace it with another button or block

Possible issues:

1) A powered button cannot be replaced by a new powered button unless it is a different type of material. In that case, it will replace the button but maintain the amount of time the button has been pressed. This means that you can not replace a powered button and make it stay pressed.

2) Replacing a powered button with a different block and then switching it back to a powered button has the same issue where it remembers how long the button was pressed for.

3) In some circumstances, when the replaced button returns to being unpowered it is not recognized by the game as being in that state. Pressing it once will not provide an update, but pressing it a second time returns it to normal. This one is much harder to recreate.