QSortFilterProxyModel from C++ unavailable in QML unless we import QtQuick.Controls

If we expose a QSortFilterProxyModel derived class to the QML engine it doesn't work and fails with:

Unable to assign MyModel to [unknown property type]

This is on the line where I try to set the sourceModel property in QML. It starts working as soon as I:

import QtQuick.Controls 1.5

 Interesting enough it's complaining about a property of a QAbstractItemModel* type, while a QAbstractItemModel derived class, used in a view works flawlessly even without importing QtQuick.Controls. Is that by design or a bug? I didn't find the documentation which states that QtQuick.Controls are needed in order to get QSortFilterProxyModel to work in QML.

my class has a basic signature of:

class BCSortFilterProxyModel : public QSortFilterProxyModel
{

    Q_OBJECT

public:
    BCSortFilterProxyModel(QObject * parent = 0);
    ~BCSortFilterProxyModel();
    Q_INVOKABLE    void    setSourceModel(QAbstractItemModel * sourceModel);
    Q_INVOKABLE void    setMultiFilter(const QVariantMap &filter);

    Q_PROPERTY(QAbstractItemModel* sourceModel READ sourceModel WRITE setSourceModel)
    Q_PROPERTY(QVariantMap multiFilter READ multiFilter WRITE setMultiFilter)
    
    QVariantMap multiFilter() const;
    QAbstractItemModel* sourceModel() const {return dataModel;}
    
    
protected:
    bool filterAcceptsRow(int source_row, const QModelIndex &source_parent) const;

private:

    BCItemModel                *dataModel;

    QMultiMap<int, QString>    mFilter;

}

 .. registered to QML with ...

qmlRegisterType<BCSortFilterProxyModel>("BecozLib", 1, 0, "BCSortFilterProxyModel");

and used like:

import BecozLib 1.0

BCSortFilterProxyModel {
    id: filteredModel
    sourceModel: MyModel
    multiFilter: {"myRole": ">=100", "myRole": "<200", "mySecondRole": "=true"}
}