BUG #6192: Incorrect result from operator "overlaps"

The following bug has been logged online:

Bug reference:      6192
Logged by:          Incorrect result from operator "overlaps"
Email address:      wolfmoon@o2.pl
PostgreSQL version: 9.0.4
Operating system:   Debian/Sid
Description:        Incorrect result from operator "overlaps"
Details:

SELECT ('2011-08-31'::date,'2011-08-31'::date) overlaps
('2011-08-1'::date,'2011-08-31'::date);
Returns false, should return true.

SELECT ('2011-08-31'::date,'2011-08-31'::date) overlaps
('2011-08-1'::date,'2011-09-1'::date);
Returns true, as it should.

SELECT ('2011-08-31'::date,'2011-08-31'::date) overlaps
('2011-08-31'::date,'2011-09-1'::date);
Returns true, as it should.

Tested in versions 8.3.14, 8.4.7 and 9.0.4.