Focus chain in qwidget and qquickwidget cause GUI frozen

1, Create a qwidget call it "Root"

2,create another qwidget, and set its parent to "Root". let me call it "child Widget",add buttons on it, set the focuspolicy of the buttons to strongfocus. set one button's focus to true.

3,create another qquickwidget, set its parent to "Root",let me call it "chid quickwidget".

4, add Rectangle to child quickwidget. set the focus of the rectangle to "true", set activeFocusOnTab to "true".

5, run the application.

6, press tab to switch focus, the focus will follow the focus chain, and go to the child quickwidget ,then press tab, will cause gui frozen. And it will print following sentence endlessly.

"qt.quick.focus: QQuickItemPrivate::nextPrevItemInTabFocusChain: from: MainScreen_QMLTYPE_1(0x28a7870, parent=0x25caba0, geometry=0,0 800x600)
qt.quick.focus: QQuickItemPrivate::nextPrevItemInTabFocusChain: current: MainScreen_QMLTYPE_1(0x28a7870, parent=0x25caba0, geometry=0,0 800x600)
qt.quick.focus: QQuickItemPrivate::nextPrevItemInTabFocusChain: from: QQuickMouseArea_QML_2(0x28a7a90, parent=0x28a7870, geometry=0,0 800x600)
qt.quick.focus: QQuickItemPrivate::nextPrevItemInTabFocusChain: current: ButtonView_QMLTYPE_0(0x28c00e0, parent=0x28a7870, geometry=0,0 800x600)
qt.quick.focus: QQuickItemPrivate::nextPrevItemInTabFocusChain: from: MainScreen_QMLTYPE_1(0x28a7870, parent=0x25caba0, geometry=0,0 800x600)"

 Please see the attachment.

I find that, when I transfer the focus between qwidget and qquickwidget, , it will always cause a frozen.

Test environment: Ubuntu 16.04