Action

In the man page for passwd, you see the following:

If all requirements are met, by default, the passwd(1) command consults /etc/nsswitch.conf to determine which repositories need a password update. It searches the passwd(4) and passwd_compat entries. The sources (repositories) associated with these entries are updated. However, the supported password update configurations are limited to the following five cases. Failure to comply with the configurations prevents users from logging in to the system.

passwd: files
passwd: files nis
passwd: files nisplus
passwd: compat (==> files nis)
passwd: compat (==> files nisplus)
passwd_compat: nisplus

The passwd(1) man page does NOT say that you can use the line: passwd_compat: nis. passwd(1) works exactly as described in the man page.