Incorect implementation UnExecute method in CommandPattern

[ghost]

https://github.com/skimedic/presentations/tree/master/Patterns/BehavioralPatterns/Command/AddNumbersCommand.cs and AddTextCommand.cs

When we use two or more Command object, UnExecute method work incorrect. For example when we add text, number and text and we want to undo last change for numberCommand we remove string (which have length of added number) from global StringBuilder object

Look at this code

            var text1 = "abc";
            var text2 = "defgh";
            var numb1 = "1234";

            var controller = new Controller();

            var addNumbCommandReference = controller.AddCommand(new AddNumbersCommand());
            var addTextCommandReference = controller.AddCommand(new AddTextCommand());           

            controller.GetCommandAt(addTextCommandReference).Execute(text1);
            controller.GetCommandAt(addNumbCommandReference).Execute(numb1);
            controller.GetCommandAt(addTextCommandReference).Execute(text2);
            
            controller.GetCommandAt(addNumbCommandReference).UnExecute();

            //Output
            //abc1234d
            //Expected:
            //abcdefgh