Android: Model bound Spinner resets to first value in its entry list

Question

I use Androids binding to populate my Spinner and set the selected item in the model. This works fine so far. But when I load a model with previously set Spinner value it gets always set to the first item in the Spinners list.

This is the Spinners excerpt from the layout file:

<Spinner
    android:id="@+id/typeSpinner"
    android:layout_width="match_parent"
    android:layout_height="@dimen/spinner_height"
    android:layout_marginEnd="16dp"
    android:entries="@{obj.CREATOR.TYPES}"
    android:selectedItemPosition="@={obj.toInt(obj.type)}"/>

And the conversion methods used for the binding:

@InverseMethod("toPhoneType")
fun toInt(@TYPE phoneType: String): Int {
    return TYPES.indexOf(phoneType)
}

fun toPhoneType(@TYPE ordinal: Int): String {
    return TYPES[ordinal]
}

I found this old post, but the (accepted) solution already applies to my code.