BUG #12872: Inconsistent processing of interval values

The following bug has been logged on the website:

Bug reference: 12872
Logged by: Jan Mate
Email address: jan(dot)mate(at)inf-it(dot)com
PostgreSQL version: 9.4.1
Operating system: Debian GNU/Linux 7
Description:

Postgresql 9.4 documentation says:

Interval values can be written using the following verbose syntax:

[(at)] quantity unit [quantity unit...] [direction]

but it works ONLY if a unit is used exactly once, e.g.:

testdb=> SELECT (now()-' +5 days -12 hours -1 second +1 week'::interval) AS
tstz;
tstz
-------------------------------
2015-03-05 11:36:08.646603+01
(1 row)

works, but:

testdb=> SELECT (now()-' +5 days -12 hours -1 second +1 day'::interval) AS
tstz;
ERROR: invalid input syntax for type interval: " +5 days -12 hours -1
second +1 day"
LINE 1: SELECT (now()-' +5 days -12 hours -1 second +1 day'::interva...

generates an error. Yes, I understand that writing '+5 days +1 day' is
"stupid" but it conforms the syntax in the documentation.

JM