app.userInteractionLevel ignored?

I've tried adding the following to my script but it appears to have no effect at all in CS5 on Windows 7.

app.userInteractionLevel = UserInteractionLevel.DONTDISPLAYALERTS;

Does this still work for anyone else?

The following example displays the alert when I execute it.

#target Illustrator
app.userInteractionLevel = UserInteractionLevel.DONTDISPLAYALERTS;
alert('Hi there!');
app.userInteractionLevel = UserInteractionLevel.DISPLAYALERTS;