Setting an A recard in enom registery not working

I need to understand
I registered a using the domain mapping plugin from my multi site and the domain was registered and mapped.

enom used thier name servers and added an A record with the dedicated ip address in the host settings the domain was mapped as it should be

now here is what is blowing me mind
I have another domain that was rederected from an external hosting account using an a recored to the dedicated IP address the domain was redirected and mapped to the Muilti site
and worked fine.
after seeing how the domain host record was set up when I registered the domain with the mapping plugin I decided to change in enom using enoms default name servers and adding an A record in the Host Records I saved the settings and forgot about it and now I fond that the domain is not redirecting to the mutil site

so the questin I have what does the mapping domain plug do that I did not do when I changed the domain settings