back-button not processed by Qt when certain flags set on Main Window

It's all described here

When certain flags are set

• Qt.WindowTitleHint
• Qt.WA_TranslucentBackground
• (~Qt.WA_ContentsMarginsRespectsSafeArea)

events for back-button and possibly other bottom/system menu items are not dispatched at all. We've tried a plethora of options, none works. We've arrived to conclusion that the culprit is the presence of ANY of the flags mentioned above.

We've tried a couple of recent devices by Samsung/ Huawei / HTC all are affected.

What's most likely wrong: as described within the thread mentioned above we haven't dived deeper due to a lack of debug-symbols for private QT's internals , but pin-pointed that  QGuiApplicationPrivate:processKeyEvent() gets fired in all cases. From the first looks there's lots of custom processing related to back-button (when targeting Android); we didn't took our time to enable for stepping through these instructions but for some reason, when the above flags are present, the event is not propagated  further i.e. the notify() never gets called.