End customer owns 2 accounts in OSA. When transferring a domain from one account to another, hosting service for transferred domain was removed automatically from the source account and another hosting service for the domain was created for the target account.
There is no internal domain transfer and having the same domain under 2 subscriptions is not supported at all. By design, fundamental limitations of OSA/DNS.
DNS servers registered in OA would be responsible for DNS hosting for both accounts/vendors, it's impossible to add a domain twice within the same installation as there are restrictions in OA/BA and also DNS server regarding duplicate domain records. Also domain registrars approves domain transfer which means that the domain that is transferred should be managed only by the new account.
Such behavior is by design of OA/BA.
A feature request with id #POA-94714 has been submitted to the Maintenance Team so please contact your Account Manager in order to clarify the status of this request.
As a workaround you should backup the content of the domain before the transfer and manually upload this content to the destination account domain.