This is a similar issue to the post below. I'm even going to copy and paste the description of the problem because it's exactly what's happening to the UC560 I'm supporting:
When we recieve an external call and a person tries to transfer the call (without consultative transfer), the person who transfers the call can still hear the ringing sound even after the call has been completely transfered and the other person has picked it up.
This is becoming a big issue for the client, and I'm this close to just replacing the UC560, but I feel that there has to be a fix for this. Anyone else experience this same issue?