QML animation flickering in fullscreen

Fullscreen QML window on separate (nothing else is running) X server flicker on animation events.
QML window size should be exactly same as screen size, if its size is less or bigger, it doesn't flicker at all.
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Test setup:

• I attached small simple qml project
• Start separate X server, eg: "X :8 vt08"
• Modify width and height of root Rectangle to your screen size. (I haven't tested with multimonitor setup).
• Run QML viewer on new X, eg: "DISPLAY=:8 qmlscene-qt5 test2.qml" - it will flicker when you move mouse over Boxes.
• Change width of root Rectangle a bit, eg +/-1 and test again - it wouldn't flicker.