Password changes are not always “chained” by an RODC. Why?

Some password-change operations, such as a user initiating a password-change request by pressing Ctrl+Alt+Del, specifically require a writable domain controller. When the client computer detects that the RODC is not writable, it locates a writable domain controller instead. Other password-change operations, such as a user’s password expiring and when the user is prompted to change it at logon, do not specifically require a writable domain controller.