Adding and deleting as a pair is pretty much compiler-like stuff. It's not built to handle such things. It's not a programming language, it has no smarts. It just puts in what you tell it to put in. It does attempt to prevent you from doing certain bad things, like creating a second IF-THEN in the middle of one. But it's not fool proof. There's a tradeoff to allowing anything to be deleted, and then expecting after deletion that everything is OK. Delete IF-THEN parts at your own risk!