timespan weirdness (fwd)

Hi!

I need some help on the following timspan results:

create table test(d date);
insert into test values('1-5-98');	// European format

test=> select * from test;
         d
----------
01-05-1998
(1 row)


// this is OK

test=> select date(datetime(d) + '1 month'::timespan) from test;
      date
----------
01-06-1998
(1 row)


// this is OK

test=> select date(datetime(d) + '5 months'::timespan) from test;
      date
----------
01-10-1998
(1 row)


// Ooops!

test=> select date (datetime(d) + '6 months'::timespan) from test;
      date
----------
31-10-1998
(1 row)


// Ok too...

test=> select date (datetime(d) + '13 months'::timespan) from test;
      date
----------
01-06-1999
(1 row)


Any comments?

Than for your help!

	Marin



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