Challenging the validity of a transfer of an opposition: reformatio in peius ex officio examination of transfer by EPO Board

On a request for a transfer of an opposition during the courseof opposition proceedings, the Opposition Division decided toaccept such a transfer and to maintain the patent in amendedform. The opponent appealed and the proprietor challenged thevalidity of the transfer of the opposition in its reply. Didthe principle of reformatio in peius apply? Should the Boardcarry out an ex officio examination of the validity of the transfer?