"$PORTAL_MESSAGE$" not working when creating error page

[codej20]

The Captive Portal Tab under Services>Captive Portal says for Authentication Errors:

"The contents of the HTML file that you upload here are displayed when an authentication error occurs. You may include "$PORTAL_MESSAGE$", which will be replaced by the error or reply messages from the RADIUS server, if any."

I've been unable to get the error message from the RADIUS server using the "&PORTAL_MESSAGE$" variable.

Is anyone else experiencing this issue?
(I am running RC1)