Anyone had any luck configuring the hold button successfully on a Mitel 5220 SIP phone? Xfer works great. Call completion works fine both directions. Audio has been beautiful. With a working system hold button, this would be a really usable phone. The hold button does make the call appear to be on hold: the light is blinking, the other party is still silently connected, I can pick up a call on another line presence. But I can't recover the call. If I press the line button again, it just hangs up.