derive structure execute

Hi

The project structure (wbs elements) i have maintained is like this -

P.01

     P.01.SD

     P.01.MM

     P.01.PP

It's ok if I dont use Derive Structure function. At clicking on Execute from the derive menu, the structure is automatically changed to

P.01

     P.01.MM

     P.01.PP

     P.01.SD

Obviously it's sorted by alphabet sequence. Is there any configuration point controlling this behavior or that's a standard way? I've been searching the forum but no luck yet to find an answer to my problem...

kljf