PowerPivot calculated columns are not dynamic

A quick and dirty one - in attempting some clever dynamic security modelling in DAX I was warned about a gotcha in my design - that calculated columns were only evaluated when the model processed, so any approach based on calculated columns was doomed to failure. I didn't quite believe it so I decided to do a road test in PowerPivot. Using a simple data set of one Dimension and one Fact, like below: