These plugins are dynamically loaded using QPluginLoader, as with the Plug 'n' Paint example. In my plugin interface, I can call a function that supplies me with a pointer to a newly allocated base class:

GenericDataModel *mdl = mod->CreateModel("frt");

where mod is a pointer to the loaded plugin interface. GenericDataModel is a derived class of QAbstractItemModel, already confirmed to work with other models. GenericDataModel is also registered as a type with QML:

qmlRegisterType<GenericDataModel>("plugin.genericmodel", 1,  0, "GenericDataModel");

This works fine, and I then load the data into the model without any problems. I confirm with the debugger that the data is there and laid out correctly. I then register the model into QML like so:

QQmlApplicationEngine engine;
QQmlContext *ctxt = engine.rootContext();
ctxt->setContextProperty("MDLFileTest", QVariant::fromValue(mdl));

I then apply this to a custom QML view, CustomList.qml:

import QtQuick 2.7
import QtQml.Models 2.2
import QtQuick.Controls 2.2
import plugin.genericmodel 1.0

ListView {
    id: listView
    property GenericDataModel dataModel

    model: dataModel
    delegate { ... }
}

Which I then apply to a page:

CustomList {
    id: customList
    dataModel: MDLFileTest
}

When loading this from a plugin (i.e. the plugin defines a class that extends GenericDataModel, and allocates one and returns it as a GenericDataModel* to the main application), I get the QML error at runtime:

Unable to assign GenericDataModel to GenericDataModel

At this point, as far as the QML layer is concerned, I've assigned a GenericDataModel for a property expecting a GenericDataModel. However, when I do exactly the same thing, but move the header and source file for the derived class into the main application, so that it is compiled in, it works perfectly...

Can somebody explain this error to me? I've seen it before with two different types that cannot be casted, but this is an error trying to assign type X to type X! Quite strange. I have played around with the Q_OBJECT macro and gotten it to read:

Unable to assign FRTFileModel to GenericDataModel

The strange thing is, FRTFileModel is a direct descendant of GenericDataModel!

I tried to keep this question as minimal as possible, but if anyone wants me to try to create a minimal example project I can give it a go as well.
Thanks!