Bug #872: Cursor scrolling

Artur Zajac (azajac(at)student(dot)uci(dot)agh(dot)edu(dot)pl) reports a bug with a severity of 3
The lower the number the more severe it is.

Short Description
Cursor scrolling

Long Description
There is some example in attachment. Sometimes after second fetch I had 0 rows (in other query). It seems that there is a bug in cursor scrolling or cursors doesn't let to move backward in some cases.

Sample Code
create table abc (a varchar(5),r int);
insert into abc VALUES ('FV','1');
insert into abc VALUES ('WZ','2');
insert into abc VALUES ('RW','3');
insert into abc VALUES ('PF','4');
select * from abc; ---- returns 4 rows
BEGIN;
DECLARE aaa CURSOR FOR SELECT DISTINCT ON (r) r,a FROM abc WHERE a!='';
FETCH ALL FROM aaa; ---- returns 4 rows
MOVE BACKWARD 26 IN aaa; --- returns MOVE 3 (why???)
FETCH ALL FROM aaa; ---- returns 3 rows

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