BO4 - Derived table joined to another derived table - selecting objects from each generates full outer join - not sure why

Hi,

Using bo4 sp08 and have 2 derived tables in a simple universe - these are joined to each other and the join is present in a context.

When select objects from each rather than one sql being generated as I would expect it is generating a full outer join when view the sql.

Any reason why this is the case?

Want just single sql.

Thanks