Select a custom background from the game for custom levels and not stick with the one the author selected for you.
If you start the game with the plugin it will automatically change the background by default to PaperOrange. To change that you need to edit the config files value "Selected Background" to whatever background you want.
Possible values are: None, BlueSky, BlueSkyWithClouds, Sunset, Forest, NightSky, CityScape, Farm, Windmill, Paper, PaperPink, PaperOrange, PaperGreen, PaperBlue, BlackWhite, MountainCastle, FinalExplosion
For easier usage the installation of ConfigurationManager is recommended.
I have no idea and I am not intended to fix that.