https://bugs.openldap.org/show_bug.cgi?id=10369
--- Comment #11 from elecharny@apache.org --- Ok, but still: the ldif contains both attributes, and get processed by the slapadd, resulting with the olcMultiProvider being considered as multi valued. You can delete it once, it's still present, but with one value only and all is good. If you don't delete it once, then you can't modify the database config because olcMultiProvider is seen as multivalued.
So beside the injected config being obviously wrong, there is something weird being done by the server.
I can live with it, no big deal, as I said it's documented in this issue, so "get your injected config fixed", and basta.