Minimal example:

import QtQuick 2.2

Rectangle {
    width: 360
    height: 360
    MouseArea {
        anchors.fill: parent
        hoverEnabled: true;
        onPositionChanged: {
            cursorShape = Qt.BlankCursor;
            console.log("set blank cursor", cursorShape);
        }
    }
}

Expected: That the mouse cursor is set to blank when the mouse position is changed over the application window, independent of its position when the application starts.
Reproduce: Start the app with the cursor already positioned where the rectangle will show up when the application first appears. Move the mouse and the log will report correctly that the cursor shape is set to "10", but it will not be visually blank. If, on the other hand, the cursor is moved out from the window and back in again then everything works as expected (the cursor disappears).