New Post: CheckComboBox selectedItems

Then the user wrote :
Also, "SelectedItemsOverride" Property (the actual "CheckComboBox"'s Property not the View Model's Binding Property) seems to always be "null" even though there are items selected (as reflected in the "SelectedItems" Property). I need to be able to write to and read from the whatever Property(ies) necessary to initially set / update / read the selected items in "CheckComboBox" via MVVM.