We have confirmed that the popup blocking setting is the cause of an event in which userprincipalname() cannot be retrieved correctly in the PowerBI workspace. 

It took us some time to remedy the problem because the Docs did not mention that the pop-up blocking settings prevented the updating of parameter values. 

That being said, I would like to propose that a statement be added somewhere in the document that pop-ups must be allowed, as I don't normally think that pop-ups interfere with the update process as it is running.