Hi Wei
I have just tried what you describe. I get the DOFF event, but the RFLink remains active and audio link is still up, and when I put on the headset I get a DON event.
It is easy to test.
1. Receive an incoming call to Lync client.
2. Answer incoming call with the headset.
3. Remove the headset from my ear. (DOFF event received)
4. Use your finger on the headsets mic input, noise is heard at the other end.
5. Put the headset back on my ear (DON event received)
In my case, RFLink is not disconnected at any point.
Kind regards
Simon.