> I am not quite sure what you mean by your last sentence.
Then you're safe.
> WHY do I have to do that?
In order to get the viewport to show the change. Assigning a value to the .UCSIconOn property sets a bit somewhere but does nothing else. Assigning a value to the .ActiveViewport property causes that value and others to be read and the results displayed. This lets you change several things about a viewport without updating the display after each change.