Arrows trigger wood buttons under spawn protect

Players are able to activate a wood button under spawn protect using an arrow shot from a bow.

They cannot press the button by hand, which is correct behavior. They also cannot shoot or press a stone button. (also correct)

What I expected:
Spawn protect would prevent an arrow from activating a wood button.

What I observed:
I watched a player open my iron door at spawn using an arrow by shooting the wood button placed on a block next to it.

How to recreate:
As an operator, place an iron door in an area covered with spawn protect. Place a block next to it, and place a wood button that block. Log in as a non-operator, and fire an arrow at the wood button using a bow. The door will open.