You can try to disable "Auto capture keyboard" in the Input section of the Global Preferences. This should give you the desired behavior. Please note that in this case even most of the F-keys aren't send to the guest.
喜好設定->Input->自動擷取鍵盤(不要選取)
喜好設定->Input->自動擷取鍵盤(不要選取)
