Rendering of QML items is not always respecting the z order when using GL_NV_ path_rendering extension

Rendering of QML items is not always respecting the z order on some setups, although the Z order is indicating that it is correct the actual result is different to what is expected.

If the scene contains a Shape element and running on hardware that supports the GL_NV_path_rendering extension, then the z order is not always respected.

The attached case will fail in this scenario, but will behavior correctly if the Shape node is changed to:

    Shape 
    {
        vendorExtensionsEnabled: false
        z: -1
    }