Strictly speaking libpam-ldap isn't a dependency to libnss-ldap. Instead it listed as a Recommended.
From Intrepid and forward Ubuntu automatically installs Recommended packages. Still, there is a difference compared to if it had been a pure dependency. This way you can still remove libpam-ldap (afterwards) without libnss-ldap being removed too.
Strictly speaking libpam-ldap isn't a dependency to libnss-ldap. Instead it listed as a Recommended.
From Intrepid and forward Ubuntu automatically installs Recommended packages. Still, there is a difference compared to if it had been a pure dependency. This way you can still remove libpam-ldap (afterwards) without libnss-ldap being removed too.
Do you still consider this a bug?