JDE1 - WOrk order creation with Blank Work order number

In some of the instance , when creation the Work order in E1(P48013) , after entering all details , along with the attachment , when saving the Work order transaction , it does not give any error though , it also do not generate any work order number , which eventually creates a record into media object table for a WO with blank Work order number , which causes a Auto attachment for further work order created in the system.  I know how to fix the auto attachment issue in case of Work order...   But want to know , why