It's a lot of opened bugs here about background process's window activation under windows. The problem is in SetForegroundWindow function. Correct behavior described in Remarks section but not all section works as described. But here is well-known solution AttachThreadInput.
SetForegroundWindow used in
which used from QWindow::requestActive() and QWidget::activateWindow()
I think we should implement this workaround.
I have tested this solution under Windows 7 x64 and it works!