commerce_payment_transaction theme hook does not have an actual theme implementation

The commerce_payment module defines a theme hook 'commerce_payment_transaction', but it doesn't define a theme_commerce_payment_transaction function or a template. The fact that this still "works" is somewhat surprising to me since I'm relatively certain that this is not intended behaviour - maybe I'm wrong and you can correct me on this. In my case, it caused some very interesting issues when I tried to customize the transaction display with a hook_preprocess_commerce_payment_transaction implementation (which doesn't work).

I think, the module should provide a reasonable default theme implementation along the lines of

function theme_commerce_payment_transaction($variables) {
  return render($variables['content']);
}