Is this a known bug?

for select id,something from wtreestore into :id, :something do
begin
update demo set something = (select something from demo where
id = (select max(id) from demo where id < :id))
where id = :id;
end

Doesn't change anything, whereas:

for select id,something from wtreestore into :id, :something do
begin
select max(id) from demo where id < :id into :workaround;
update demo set something = (select something from demo where
id = :workaround)
where id = :id;
end

Works as expected.

Thanks,

John