Decision cube components generates an SQL query.
You can see it by clicking on 'SQL' property of your TDecisionCube component.
This query often like:
SELECT x, y, SUM(z)
GROUP BY x, y
And the Decision cube component will assume that x and y values will come in the right order.
But the AS/400 SQL engine never sorts the result if you don't ask it so.
So, to be sure to have correct results, just modidy the SQL query like this :
SELECT x, y, SUM(z)
GROUP BY x, y
ORDER BY x, y