What model IP phone and what software revision?
I'm guessing you have MPS enabled (its there by default in 4.4 software), if you are using this and have a version of software on the ITP phone (or a ITP-50xxD handset) you will have this problem.

Either disable MPS (not my choice) or upgrade the handset version to the latest available (3.37 for ITP-51xx series down here) to support MPS