Inline component results in "unknown type"

I create custom grouped properties in QML by creating a component like so:

// MyProps.qml
    property real
    property real y
}

And then I can use it:

// MyComponent.qml
Item {
    id: root
    property MyProps myProps: MyProps {}
}

I tried replacing MyProps.qml with an inline component:

// MyComponent.qml
Item {
    id: root
    component MyProps : QtObject {
        property real x
        property real y
    }
    property MyProps myProps: MyProps {}
}

However this gives me an error on the myProps declaration line:

Cannot assign to property of unknown type "MyComponent_QMLTYPE_1".*

From the documentation it sounds like inline components should behave identical to components defined in a separate file so I suspect this might be a bug. Is this not accurate? If not how are they different? (maybe this can be clarified in the documentation?)