You have to select the AI mode, and then select Subtract, as shown. If you leave it on Add, it, well, it adds something. You can tweak the result; it gives you several options. Just because it gives you a Bitcoin when you tell it to add something random doesn't mean you have to accept it. RTFM

You told it to put something in that spot and you didn't specify what. Then you complain that it did what you told it to. Geez.