BUG #12242: No error - if there is no comma seperator

The following bug has been logged on the website:

Bug reference: 12242
Logged by: Onkar Gaonkar
Email address: omkar1103(at)gmail(dot)com
PostgreSQL version: 9.3.3
Operating system: Windows
Description:

Below script does not throw error
=======================================
SELECT
claim_status,
claim_key
FROM tbl_claim
WHERE claim_key IN
(
'1140799265'
'2129945595'
)
=======================================

Throws Error
=======================================
SELECT
claim_status,
claim_key
FROM tbl_claim
WHERE claim_key IN
(
'1140799265' '2129945595'
)

ERROR: syntax error at or near "'2129945595'"
LINE 7: '1140799265' '2129945595'
^
********** Error **********
ERROR: syntax error at or near "'2129945595'"
SQL state: 42601
Character: 113
=======================================