Actions are classes and as all classes in c#, they are passed by reference. That means that if you keep adding the same instance of a class in a list, all actions in that list will point/reference to the same original action instance (not a copy). This is just standard in C# (and most OOP languages).
With that said, I think the way you try to accomplish your goal is a bit complicated and I would advice against adding ActionTasks in the graph dynamically this way.
Can you please describe your END GOAL and what you are trying to accomplish, so that I can advice with an alternative solution?
Gavalakis
