Keyboard grab does not work on popup windows

When I run the manual test for popupwindow key events (Qt5.3.0\src\qtquickcontrols\tests\manual\popupwindowkeyevents.qml) on Windows, key events are not sent to the popup window. I looks as if setKeyboardGrabEnabled() does not have any effect.

Ideally I would like to use the PopupWindow from QtQuick.Controls.Private. Do you plan to make it part of QtQuick.Controls directly? I need to show a custom qml scene in a context and drop down menu, and this class would be perfect. But no matter if I use this or a custom popup class, I always run into the problem that a popup window that does not draw the focus from its parent window does not get key events, even when calling setKeyboardGrabEnabled(true) on it.

I wonder if this is related to this bug: QTBUG-39156.

I attached the test from the qtquickcontrols folder I am referring to.