Check your settings on the C.O. ports, as Russ suggested. Also, check what your minimum message length is set to.

DO NOT touch the Disconnect Notification setting. This bit me one time, and never again. It's my understanding that is was there only for use with Comdial's proprietary Air Impact wireless phones (not the Scout or Scout II), and should not be used for anything else. Make sure this setting remains disabled. This would be a station setting, not a C.O. port setting. The C.O. port setting (Disconnect Supervision) should remain turned on, as you indicated it was.

Justin