deleting user in ldap should not delete attribute displayName. This is also an attribute of the inetorgperson schema. Using ldap delete dn is a workaround at the moment. See this log:

[2006/08/27 19:35:00.304133, 10] lib/util_pw.c:getpwnam_alloc(76)
  Got bjacke_test from pwnam_cache
[2006/08/27 19:35:00.304154, 5] lib/username.c:Get_Pwnam_internals(108)
  Get_Pwnam_internals did find user [bjacke_test]!
[2006/08/27 19:35:00.304178, 10] passdb/lookup_sid.c:sid_to_uid(1274)
  sid_to_uid: S-1-5-21-1621506835-96080155-59529505-1003 -> 17695
[2006/08/27 19:35:00.304209, 3] passdb/pdb_ldap.c:ldapsam_delete_sam_account(1687)
  ldapsam_delete_sam_account: Deleting user bjacke_test from LDAP.
[2006/08/27 19:35:00.304245, 5] lib/smbldap.c:smbldap_search_ext(1179)
  smbldap_search_ext: base => [dc=samuc,dc=de], filter => [(&(uid=bjacke_test)(objectclass=sambaSamAccount))], scope => [2]
[2006/08/27 19:35:00.305205, 10] passdb/pdb_ldap.c:ldapsam_delete_entry(430)
  ldapsam_delete_entry: deleting attribute sambaSID
[2006/08/27 19:35:00.305251, 10] passdb/pdb_ldap.c:ldapsam_delete_entry(430)
  ldapsam_delete_entry: deleting attribute sambaPrimaryGroupSID
[2006/08/27 19:35:00.305285, 10] passdb/pdb_ldap.c:ldapsam_delete_entry(430)
  ldapsam_delete_entry: deleting attribute sambaKickoffTime
[2006/08/27 19:35:00.305325, 10] passdb/pdb_ldap.c:ldapsam_delete_entry(430)
  ldapsam_delete_entry: deleting attribute sambaAcctFlags
[2006/08/27 19:35:00.305363, 10] passdb/pdb_ldap.c:ldapsam_delete_entry(430)
  ldapsam_delete_entry: deleting attribute sambaPasswordHistory
[2006/08/27 19:35:00.305394, 10] passdb/pdb_ldap.c:ldapsam_delete_entry(430)
  ldapsam_delete_entry: deleting attribute sambaPwdCanChange
[2006/08/27 19:35:00.305432, 10] passdb/pdb_ldap.c:ldapsam_delete_entry(430)
  ldapsam_delete_entry: deleting attribute sambaPwdMustChange
[2006/08/27 19:35:00.305472, 10] passdb/pdb_ldap.c:ldapsam_delete_entry(430)
  ldapsam_delete_entry: deleting attribute sambaLMPassword
[2006/08/27 19:35:00.305510, 10] passdb/pdb_ldap.c:ldapsam_delete_entry(430)
  ldapsam_delete_entry: deleting attribute sambaNTPassword
[2006/08/27 19:35:00.305545, 10] passdb/pdb_ldap.c:ldapsam_delete_entry(430)
  ldapsam_delete_entry: deleting attribute sambaPwdLastSet
[2006/08/27 19:35:00.305582, 5] lib/smbldap.c:smbldap_modify(1363)
  smbldap_modify: dn => [uid=bjacke_test,ou=Users,dc=samuc,dc=de]
[2006/08/27 19:35:00.305995, 10] lib/smbldap.c:smbldap_modify(1377)
  Failed to modify dn: uid=bjacke_test,ou=Users,dc=samuc,dc=de, error: Object class violation (attribute 'displayName' not allowed)