we have Auto numbering, update not allowed option set for customer numbering then if we click on cr

Summary:

Customer Account numbering changed from manual to automatic

Content (required):

 we have Auto numbering, update not allowed option set for customer numbering then if we click on create the customer (manual UI) then customer account number generated e.g 8001 but if we cancel the customer generation then again click on create customer then system is generating customer account # 8002. Although number is automatic generated but there is gap in that. Actually it should give 8001 as this number is not utilized by oracle. Is it normal behavior? So there will be in gap in sequencing in this case. Pls shed some more light on this.