NativeText rendering is broken on Linux

Text elements incorrectly painted when using NativeText renderType on linux.

It looks like the top pixel row from the glyph cache is omitted regardless of pixelSize and it happens at half pixel coordinates.

Simple example:

 
import QtQuick 2.0

Item{
    width: 100
    height: 100
    Text {
        y:10.5
        renderType: Text.NativeRendering
        text: "hello"
    }
}