BUG #10316: Alter table rename fails if the "new name" starts with '_'

The following bug has been logged on the website:

Bug reference:      10316
Logged by:          Parthi
Email address:      parthibanp2@gmail.com
PostgreSQL version: 9.3.2
Operating system:   Mac OSX 10.9.2
Description:

Hi I'm facing one peculiar behaviour(bug?) with Alter table rename query
SQL.

-- I have created one new table with name t1

test=# \d
No relations found.
test=# create table t1 (name varchar(10));
CREATE TABLE

-- After that i tried to rename 't1' table as '_t1', now the Postgres server
saying '_t1' is already exists. i'm sure there is no other table in the
database other than 't1'.

test=# alter table t1 rename to _t1;
ERROR:  type "_t1" already exists

-- Now i renaming table from 't1' to '__t1' and again i renaming from '__t1'
to '_t1' now its working.

test=# alter table t1 rename to __t1;
ALTER TABLE
test=# alter table __t1 rename to _t1;
ALTER TABLE

-- Again i renamed '_t1' to 't1', once again i tried the first query , now
its working.

test=# alter table _t1 rename to t1;
ALTER TABLE
test=# alter table t1 rename to _t1;
ALTER TABLE


May i know , why the rename query failed initially? if it is bug then how
the same query succeeded during second time?