vCenter 5.5 SSO and a child domain as identity source

Hello,

we have an Active Directory with 2 domain in the forest.

One root domain "contoso.local" and one child domain "belgium.contoso.com"

Only the child domain contains resources (users and computers).

When adding the child domain as an AD identity source, automatically SSO converts it to the root domain.

The login is then working, but we must use the form user@childdomain or childdomain\user, even if we set the default SSO domain to be the root.

Any idea how to add the child domain as the default identity source, so we are not forced to enter the domain name in the login ?

Thanks