we have upgraded a site to 4.0.7, we have noticed when we answer the call on a 5410, (which has has software upgrade), and has twinning enabled to a mobile. when answers in headset, or speakerphone mode, all good, when call finishes, the phone displays "disconnected" and tones for 32 seconds, then times out, back to idle state, never did this before, does when he answers via line appearance key, or headset/speaker, any ideas