Sub Domains problem, i don't understand

I will take an exemple to expose my problem.

I have a domain :
When i create it, virtualmin create a bind record (

I would like to create a sub-domain :
I create it with virtualmin. BUT, Virtualmin create a new bind record for sub-domain, it create this file : Why this ? this type of bind sub-domains record can not be usable with secondary bind servers declarations !

Why virtualmin don’t add A or CNAME record directly in for bind ?

Many thanks for help.