SharePoint 2013 - People picker: Round robin problem with multiple domains

Environment

Old: olddomain.local

New: Forest (contoso.local) with 2 domains:

• newdomain.contoso.local (User)


• newservice.contoso.local (Servideaccounts, Server)

New and old domain are still existing with a one way trust.

I configured the peoplepicker with a user account for every domain.

The SharePoint Server is in the newservice.contoso.local domain

My problem:

Any ideas to solve this problem?

Thank you in advance!