Test case:

create table t (n integer);

insert into t values (1);
insert into t values (2);
insert into t values (3);

commit;

create index t_n on t (n);

set term !;

execute block returns (n integer)
as
  declare x integer;
begin
  update t set n = n where n = -1;
  n = row_count;
  suspend;

  update t set n = n where n = (select -1 from rdb$database);
  n = row_count;
  suspend;

  update t set n = n where n = -1;
  n = row_count;
  suspend;

  for select 1 from t where n = -1 into x do
  begin
  end
  n = row_count;
  suspend;

  for select 1 from t where n = (select -1 from rdb$database) into x do
  begin
  end
  n = row_count;
  suspend;

  delete from t where n = (select -1 from rdb$database);
  n = row_count;
  suspend;
end!

set term ;!

Returns:
0
1
0
0
1
1

Should return:
0
0
0
0
0
0