Strange results with date/interval arithmetic

I am seeing strange results from date/interval computations involving
months.

I get the correct answers because I have a negative setting relative to
GMT.  Here are my results with TZ=EST5EDT:test=> select '2001/3/1'::date - '1 month'::interval;        ?column?
------------------------2001-02-01 00:00:00-05(1 row)
 

With GMT it is OK too:
test=> select '2001/3/1'::date - '1 month'::interval;        ?column?        ------------------------ 2001-02-01
00:00:00+00(1row)
 

However, with GMT+1 I see a big failure:
test=> select '2001/3/1'::date - '1 month'::interval;        ?column?        ------------------------ 2001-01-29
00:00:00+01(1row)
 

Why does it say 2001-01-29?

This is interesting:test=> select '2001/7/1'::date - '1 month'::interval;        ?column?
------------------------2001-05-31 00:00:00+02(1 row)test=> select '2001/8/1'::date - '1 month'::interval;
?column?       ------------------------ 2001-07-01 00:00:00+02(1 row)
 

Because August and July have the same number of months, it worked.  I am
going to research this but someone may know the solution already.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
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