I'm not sure if this is a bug or a design, but I'm inclined to think it's a bug.

If it is a bug, then it should change command models when I change the default model.

If this is not a bug, then a better approach would be either:

i) when I change the global model, ask me if I want to change the custom models accordingly.

ii) for commands, provide a model option as "default". That way, if a user selects command model as "default", any changes made to global model will be reflected in commands. And if someone wants to separate global and default, they can still do that.