Sub Domains problem, i don't understand

I will take an exemple to expose my problem.

I have a domain : toto.com When i create it, virtualmin create a bind record (toto.com.hosts)

I would like to create a sub-domain : test.toto.com I create it with virtualmin. BUT, Virtualmin create a new bind record for sub-domain, it create this file : test.toto.com.hosts. 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 toto.com.hosts for bind ?

Many thanks for help.