Navigate to HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\System\DNSclient.
If the Primary DNS Suffix key contains a value, then the computer will not automatically adjust to the new primary DNS suffix.
Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters.
Verify whether the value of REG_RWORD SyncDomainWithMembership is 0x1. This value indicates that the primary DNS suffix changes when the domain membership changes. Any other value means that the computer will not automatically adjust to the new primary DNS suffix.