Behavior of deriving from extended type inconsistent

Say a C++ type is registered to the QML engine with an extended type:

qmlRegisterExtendedType<Type, ExtendedType>(uri, 1, 0, "Type"); 

Furthermore, another C++ type public derives from Type, and is registered to the QML engine too:

qmlRegisterType<DerivedType>(uri, 1, 0, "DerivedType");

should the DerivedType in QML 'inherit' the additional properties of ExtendedType, or not?

Currently the behavior is inconsistent. That is, by default it inherits - unless there's another registration for another major import afterwards:

// this breaks DerivedType.data
qmlRegisterType<Type>("XXX", 3, 0, "TypeXXX");