In the declarative plugins, properties are marked as read-only even when they are clearly not, for example

http://doc.qt.nokia.com/qtmobility-1.2/qml-deviceinfo.html

explicitly says

"Note: To use notification signals, you need to set the monitor* properties to true"

and has on the same page listed all monitor* properties as read-only in the detailed description. The source also suggests it's a writable property, for example

Q_PROPERTY(bool monitorBatteryLevelChanges READ monitorBatteryLevelChanges WRITE startBatteryLevelChanged)

I see similar bug-reports like QTBUG-20739 but those seem to be for components or things based on QML whereas the underlying classes here are pure C++