subsequent documents deleted

Dear Experts,

If bill,PGR,Delivery documents are canceled/reversed/deleted, can we delete sales order now? In our system, in one of cases the system allows this to happen (i.e. sales order can also be deleted) while in other instance it does not allow the sales document to be deleted, however it allows to close the document.

Is there any setting that controls the procedure?

Please advise.

Regards,

Randhir