BUG #8333: Conversions from TEXT to range types are not immutable

The following bug has been logged on the website:

Bug reference: 8333
Logged by: Alex Bolenok
Email address: quassnoi(at)gmail(dot)com
PostgreSQL version: 9.2.4
Operating system: Fedora 19
Description:

SET lc_messages TO 'en_US.UTF-8';

DROP TABLE IF EXISTS
mytable;

CREATE TABLE
mytable
(
id INT NOT NULL PRIMARY KEY,
vtext TEXT NOT NULL,
vrange INT8RANGE NOT NULL
);

INSERT
INTO mytable
SELECT 1, t, t::INT8RANGE
FROM (
VALUES
('[1, 10]')
) q(t);

CREATE INDEX
ix_mytable_vrange
ON mytable
USING GIST (vrange);

CREATE INDEX
ix_mytable_vtext
ON mytable
USING GIST ((vtext::INT8RANGE));

--

SET
DROP TABLE
psql:<stdin>:12: NOTICE: CREATE TABLE / PRIMARY KEY will create implicit
index "mytable_pkey" for table "mytable"
CREATE TABLE
INSERT 0 1
CREATE INDEX
psql:<stdin>:30: ERROR: functions in index expression must be marked
IMMUTABLE

--

I expected the second index to be created as well.