This is normal good, expected behavior. The only thing that should
write to the slaves is the master, which will include the Operational
attributes. (including structuralObjectClass) Clients writing to the
master should not include structuralObjectClass for that same reason;
it is an internal-use attribute that client software should not touch.
If you need to play special games like having external software write
to a slave, you'll need to understand what these operational
attributes are and what semantics are associated with them.
If you need to replicate via slurpd to a slapd that believes itself to
be a master, you'll need to strip these attributes out. The
slapd.conf(5) manpage has the details on how to specify a list of
attributes to include or exclude for each replica...
If you are loading LDIF via ldapadd that was dumped via slapcat or
similar, you'll also need to strip these attributes out or load via
the offline tool slapadd.