https://bugs.openldap.org/show_bug.cgi?id=9888
--- Comment #4 from Howard Chu hyc@openldap.org --- Also note that the OID is part of the index key, so reusing OIDs for different attributes will absolutely corrupt indices.
This is a long standing rule - OIDs of existing attributes must never be changed or reused for different attributes. If you're doing schema changes of that sort, you must always assign entirely new OIDs to ever changed attribute.