ComboBox element cannot be navigated using keyboard when the combo is not editable

An interface created using QML components for a desktop application should be navigable with the keyboard. Currently a ComboBox element with editable set to false cannot be navigated with the keyboard. Only a mouse click on the ComboBox allows to set the focus on the ComboBox and from that point on the keyboard navigation is possible. If the ComboBox is editable, the keyboard navigation is possible as expected.