My earlier question did not appear. The last message from the a/c was "Ok - roger that" Isn't that rather an unusual response when leaving one ATC for another, surely you always give your callsign?
This RT exchange certainly sounds non-standard. Was the aircraft transmission spoken by someone in the flight deck other than the pilots? Would an ATC transcript of the handover yield more clues?
Apologies if this suggestion has already been posted.