EPDM auto-numbering configurations

Hello

I encountered a small problem on using serial numbers automatically naming part files.

My issue is as follows: i am creating a part. It gets, on save, a part number following the serial number set up for that. Save, check in.

Later on i need to add  configurations to this part. Now something strange is happening. The first one gets a new number but after that the auto-numbering stops working.

Any ideea what I am doing wrong?