XCB: high DPI scaling not numerically stable

When resizing a QWindow with devicePixelRatio > 1, the resulting native size will map to a different size than the original. The attached program is stable at dpr 1, but grows continuously at dpr 2. This program is not a realistic use case, but it reproduces a problem with the following Qt Quick application:

import QtQuick 2.4
import QtQuick.Window 2.2

Window {
    height: 360
    width: height * 2
    visible: true
    MainForm {
        anchors.fill: parent
        mouseArea.onClicked: {
            Qt.quit();
        }

    }
}