problem with Avaya IPPhone

Hi,
We are facing problem with call forward in Avaya 4620 IPPhone.
Scenario is : IP Phone 1 and IP Phone 2 are registered with a redirect server.
IPP1 sends an INVITE to RServer. It sends 302 with IPP2 details in contact header. This means contact IPP2 but IPP1 keeps calling RServer.
Anyways to make it work ? Any configuration is required to be changed ?
PLease help us out.

 

Thanks and regards,

Viswaraj.