Applying the principles expounded in G 9/92 and G 4/93 (OJ 1994, 875) the board concluded in T 856/92 that in a case where the patentee and sole appellant appealed only in respect of some of the claims held allowable in the opposition division's interlocutory decision, neither the board nor the opponent might challenge those claims not questioned by the appellant.
In T 598/99 the board observed that the principle of reformatio in peius applied so as to prevent a sole appellant being put in a worse situation than he was in before he appealed. Where the patentee was the sole appellant, the principle could not serve to protect the opponent/respondent from being put in a worse situation than he was in before the appeal (G 9/92, OJ 1994, 875 and G 4/93, OJ 1994, 875). Indeed, whenever a sole patentee was successful in his appeal against the revocation of his patent, the opponent would be in a worse position than before. The fact that the opponent was not entitled to appeal against the decision to revoke the patent was immaterial in that respect.
The board in T 659/07 found that the applicability of the legal principle of the prohibition of reformatio in peius depends on the procedural status of a case, which had therefore to be examined prior to the substantive merits of a request. Where the patentee is the sole appellant, the board further held that the patent as maintained by the opposition division in its interlocutory decisions, cannot be objected to by the board, either at the request of the respondent/opponent or ex officio, even if the patent as maintained would otherwise have to be revoked on the ground that a feature present in both claim 1 as granted and as maintained introduces added subject-matter contrary to Art. 123(2) EPC 1973.