I tested now the Schema Management MMC (schmmgmt.msc) with creating a new objectclass for the directory. It seems to work fine but what I noticed is that the default assigned ACL's seem to be very different than those of the predefined classes.
It seemed to work fine. But when I now restarted the smbd, it immediately crashed because a certain "unable to map governsID" "failed to load class definition" WERR_DS_NO_MSDS_INTID.
Yeah, it doesn't really work - we need to do a lot more work around the schema area.
I retested this one now and get this kind of problems: ldb: Unable to load modules for /usr/local/samba/private/sam.ldb: partition_init: initialising backend for CN=Schema,CN=Configuration,DC=wallnoefer2,DC=local failed: schema_fsmo_init: failed to load class definition: CN=myclass,CN=Schema,CN=Configuration,DC=wallnoefer2,DC=local:WERR_INVALID_PARAM ldb: schema_fsmo_init: failed to load class definition: CN=myclass,CN=Schema,CN=Configuration,DC=wallnoefer2,DC=local:WERR_INVALID_PARAM ldb: module schema_fsmo initialization failed
Finally fixed with latest patches.