Private marked Tasks in Public Folder after Migration 2007 -> 2013 hidden

After the Migration of Public Folders from 2007 to 2013 some private marked tasks are hidden.

I see the item with mfcmapi but outlook doesnt show it. I think there is a problem with permission to see private marked items. But there is it possible to set this?

For example Public Delegation in Public Folder Mailbox?

Thanks fpr help