cannot cast type boolean to text?

I'm not sure if this is the right
So when I do:
    SELECT true :: text;
in psql, I get back:

ERROR:  cannot cast type boolean to text

I was wondering why this is so.  Unfortunately, the place where I hit
the problem was in a function that takes arguments of type ANYELEMENT
and wants to convert them to text.  Which doesn't make it impossible to
work around this, just more annoying.

This is Postgres 8.1.4.

Would this be something worthwhile to post to Hackers?

Brian