Why if I Reassign an Internet-based Workgroup Client to a New Site does the Client continue to stay Assigned to the original Site until it connects to the intranet?

Why if I Reassign an Internet-based Workgroup Client to a New Site does the Client continue to stay Assigned to the original Site until it connects to the intranet?

I’ve reassigned a Workgroup Client that’s Internet-based to a new Site whilst the Client is on the Internet. However, the Client continues to stay assigned to the original Site until it connects to the intranet.