[Spiker]

Somebody that created that bench graphic image didn't add the correction to the tileset for winter. I'm sure it will look better once the snow is gone. If it bothers you, just edit it yourself and it will change the image for you and nobody else unless uploaded to the server.

EDIT: I retract my statement, it's an issue with the tileset. The transparency on the 'grill' image is perfect, the issue is that after it goes through the transparent portion, there isn't the correct tile underneath it, and it shows like that. You'd have to search for the tile portion and change it, or make 2 versions of the bench.