Where the composition of an opposition division is held to be contrary to the requirements of Art. 19(2) EPC, in that two or more took part in the prior proceedings for grant, this is generally held to be a substantial procedural violation, the decision is set aside, the appeal fee reimbursed and the case remitted for fresh examination by an opposition division with a different composition (see e.g.T 251/88, T 382/92, T 476/95, T 135/12). If only one examiner took part in the prior proceedings, that examiner may not be chairman in the subsequent opposition proceedings under Art. 19(2) EPC (T 939/91).
Art. 19(2), first and second sentence, EPC refers to the participation of members of the opposition division at every stage of the grant proceedings, not only to their involvement in the final decision (T 476/95).
In cases of a breach of Art. 19(2) EPC it follows from the lack of jurisdiction of the department of first instance that the impugned decision is void ab initio. The faulty constitution of the opposition division gives rise to a substantial procedural violation and the appeal fee must be reimbursed (see e.g.T 382/92).