Usage of required properties breaks ComboBox

When writing a ComboBox delegate, the properties modelData and index become unavailable if the delegate makes use of components with required properties:

ReferenceError: modelData is not defined
ReferenceError: index is not defined

Removing the "required" keyword circumvents the problem.

Reproduction

Example project and screenshots attached. The code runs fine when removing the "required" keywords from both MyDelegate.qml and MyText.qml. When the "required" keywords are not removed, the popup breaks visually and yields the following error:

ReferenceError: modelData is not defined