Hello Christian,

Thank you for your post. I have been looking into it and I can suggest you set the EditorStyle instead of the CellValuePresenter’s like this:

<igDP:Field Name="Hvornar" Label="Hvornar">
    <igDP:Field.Settings>
        <igDP:FieldSettings EditAsType="{x:Type sys:String}" AllowEdit="False">
            <igDP:FieldSettings.EditorStyle>
                <Style TargetType="{x:Type igEditors:XamTextEditor}">
                    <Setter Property="Value" >
                        <Setter.Value>
                            <MultiBinding Converter="{StaticResource HvornaarTextConverter}">
                                <Binding Path="DataItem.Mandag" />
                                <Binding Path="DataItem.Tirsdag" />
                                <Binding Path="DataItem.Onsdag" />
                                <Binding Path="DataItem.Torsdag" />
                                <Binding Path="DataItem.Fredag" />
                                <Binding Path="DataItem.Lordag" />
                                <Binding Path="DataItem.Sondag" />
                                <Binding Path="DataItem.Periode" />
                                <Binding Path="DataItem.Hvornar" />
                            </MultiBinding>
                        </Setter.Value>
                    </Setter>
                </Style>
            </igDP:FieldSettings.EditorStyle>
        </igDP:FieldSettings>
    </igDP:Field.Settings>
</igDP:Field>

Please let me know if this helps you or you need further assistance on this matter.

Looking forward for your reply.