Having had an incident of this type a long time ago. It transpired that the previous sector had failed to hand us over and due to ducting the frequency picked up another station on the same frequency, so as far as we were concerned we could still hear the controller. (Note the change over boundaries were not as clear as they are now)
Of interest I was discussing this in a bar, when an old boy commented that once in a viking(i think) he heard Heathrow tower whilst on finals into Delhi.