T58A SCA Shared Call Appearance with Call Manager

Hello, I have two T58A's registered to csico call manager 11.5.1 with the same line configured on both phones. When I call that line, both phones ring ok, but once I answer the call on one of the phone, there is no indication that the line is busy on the second phone. How do I fix this? If I setup a cisco phone and a yealink phone the cisco phone shows the line as busy but I can't get the yealink phone to show the line as busy. I'd appreciate any help with this.

Thanks.