You might have to check your field option on this. It seems that you have defined your serial ID field to generate a value upon committing the record.
When does the auto numbering take place?
It depends on how you define your field's option. When creating an Auto-Enter Serial Number field, you have two options of when to generate its value, either On creation or On commit and the default behavior is the former.
Thanks so much, Jim Paul. I overlooked those options.