I loaded up a map from a previous snapshot version and the stairs that were already there have solid block hitboxes. You can't break blocks through the holes in the stairs. When placing a stair in the actual snapshot, the stairs' hitboxes are fine and are able to break the block through the stairs' hole.

I was able to duplicate this bug by creating a world in 14w29a and placing a stair then loading it in 14w30b. I was unable to break the blocks through the stair's hole.