strange issue with pwdAccountLockedTime

The following ldif fragment: dn: uid=melancon,ou=saclay,ou=futurs,ou=users,dc=futurs,dc=inria,dc=fr changetype: modify replace: userpassword userpassword: XXXXX - replace: gidnumber gidnumber: 5050 - replace: homedirectory homedirectory: /home/gravite/melancon - delete: pwdAccountLockedTime

causes the server to choke with error: ldapmodify: No such attribute (16) additional info: modify/delete: pwdAccountLockedTime: no such attribute

However, when removing other changes, and keeping only pwdAccountLockedTime deletion, everything works OK....

So, it is an expected behaviour than modificating operational attributes at the same time than normal attributes should fail, or is it a bug ?

openldap version is 2.3.27.