attributes rendered incorrectly

When working with the fb module, which requires adding a class of "fb_canvas-resizable", I discovered that the Sky theme does not respect the classes added in the page preprocess function, but instead forces _ to -.

http://drupal.org/node/952984

function sky_render_attributes($attributes) {
    //...
    $output = ' '. str_replace('_', '-', implode(' ', $items));
   //...
}

This seems a bit odd to me. If I add a class, I do not expect the theme to change it on me.