[midPoint] - Schema violation during processing shadow: attributeOrValueExists [3.4.1]

[Wojciech Staszewski]

Hello,

I try to make inbound mapping attributes from my custom LDAP objectClass.
I'm doing this like that:
- remove <schema> and <constraints> sections of my resource to let MP read and 
recreate all objectClasses,
- add <auxiliaryObjectClass>mycustomclass</auxiliaryObjectClass> to 
<schemaHandling> section. Save.
- After this step I see my class on the classes list and all of its attributes 
in Schema handling wizard step. So I'm using them in inbound mapping. Save, 
finish.
- Server tasks , reconciliation, Run now.

Error:
SystemException: Schema violation during processing shadow: shadow: 
uid=xxxxx,ou=People,dc=xxxxx,dc=xx (OID:013c3113-d4e8-4c7a-c434-7ec9f7bceb1c): 
Schema violation: Invalid attribute: 
org.identityconnectors.framework.common.exceptions.InvalidAttributeValueException(Error 
modifying LDAP entry uid=xxxxx,ou=People,dc=xxxxx,dc=xx: [add:objectClass: 
mycustomclass,]: attributeOrValueExists: (20))

Despite the error, attributes from mycustomclass are mapped to users, I can 
see them in user properties.

My questions:
- WHY midPoint is trying to add "mycustomclas"s to LDAP users while they 
already have this class?
- What I'm doing wrong?

Thanks :)