The dark background was fixed on Xubuntu Yakkety, and it was due to changes in the latest GTK+. As for the other bug, calling something so badly done as a clever feature doesn't make sense at all. If I want the window decorations hidden, I just go full screen with F11. Double clicking to restore is something many users won't know, and doesn't work when there are tabs enough to cover the whole tab bar. It was something designed specifically for Unity, and should be disable in any other environment.