QGeoMapObject::setZValue has no effect

Starting with 1.2.0 final release we often see QGeoMapObjects painted with the wrong z-Value.
The attached screenshots show this behaviour. The blue area hast a z-Value of 0, while the cars are located on a z-Value of 1.
However, sometimes they are painted the other way round.

We have not noticed this behaviour with 1.2.0 Technology Preview or previous versions (1.1.3).
This issue can be seen on the desktop as well as on the N900.