I'm running Office communicator public beta. Placing a call through the mediation server and out a gateway works fine. I can put the call on hold, and the gateway gets a REINVITE with a=inactive. I can resume the call, and the call resumes correctly.
If I disconnect the audio device, OC goes on hold, and sends the REINVITE to the gateway with the a=inactive correctly. When I reconnect the audio device, OC should unhold the call. Instead, it tried to put the call on hold (which it is already on hold) with a=inactive (which of course, the gateway rejects with "Call already on hold"), and reports this error in the window:
An error occurred while trying to place the call on hold. Please try again. If the problem persists, contact your system administrator. More details (ID:491)