Can't set UObjectProperty's Class Default value

[Algorithman]

If you try to set the default value of a UObjectProperty of a C# class i get the following warning:
LogProperty:Warning: Illegal TEXT reference to a private object in external package (StaticMeshActor /Game/StarterContent/Maps/Minimal_Default.Minimal_Default:PersistentLevel.Chair) from referencer (TestNochmalNeu_C /Game/TestNochmalNeu.Default__TestNochmalNeu_C). Import failed...
LogProperty:Warning: Illegal TEXT reference to a private object in external package (StaticMeshActor /Game/StarterContent/Maps/Minimal_Default.Minimal_Default:PersistentLevel.Chair) from referencer (TestNochmalNeu_C /Game/Max.Max_C:TestNochmalNeuA24BB8B142339FCD457728AE708B2890). Import failed...
LogProperty:Warning: Illegal TEXT reference to a private object in external package (StaticMeshActor /Game/StarterContent/Maps/Minimal_Default.Minimal_Default:PersistentLevel.Chair) from referencer (TestNochmalNeu_C /Engine/Transient.REINST_Max_C_25:TestNochmalNeuA24BB8B142339FCD457728AE708B2890). Import failed...
LogProperty:Warning: Illegal TEXT reference to a private object in external package (StaticMeshActor /Game/StarterContent/Maps/Minimal_Default.Minimal_Default:PersistentLevel.Chair) from referencer (TestNochmalNeu_C /Engine/Transient.REINST_Max_C_29:TestNochmalNeuA24BB8B142339FCD457728AE708B2890). Import failed...

Names:
Max = Actor which holds the KlawrScriptComponent
TestNochmalNeu_C = Name of the KlawrScriptComponent class

It won't hold (in this case) the Actor.