In J 27/94 (OJ 1995, 831) the board decided that if a declaration which was subject to a condition and therefore invalid was treated as a valid procedural act by the EPO, the EPO was not allowed later to go back on its own earlier conduct which served as a basis for the applicant's decision on how to proceed, because this would have represented "venire contra factum proprium" and thus offended against a generally recognised legal maxim.
In J 14/94 (OJ 1995, 825), the applicant had failed to pay the third renewal fee. Nevertheless, the EPO continued the examination procedure for several years without informing the applicant of any loss of rights. The board held that if, during a long period of time, the EPO by its conduct led the parties and the public to the legitimate belief that no loss of rights had taken place, the EPO could not later refer to a loss of rights which occurred several years previously as this would constitute "venire contra factum proprium" and therefore contravene the principle of legitimate expectations. In such circumstances, the late payment of a renewal fee might - by way of exception - be considered as having been made in time if the EPO had not informed the applicant of the outstanding payment, had accepted later renewal fees without objection and had continued the examination proceedings for several years.
In J 18/96 (OJ 1998, 403) the board accorded a filing date to protect an applicant's legitimate expectations, although he had not fulfilled a requirement under Art. 80 EPC 1973. By issuing a communication under R. 85a EPC 1973 (deleted in EPC 2000), the Receiving Section had given him the impression that his application was validly filed (see also J 5/89).
In J 1/08, the Legal Board of Appeal concluded that the mere fact that for an admittedly extremely long time period (from August 2004 to March 2007) the EPO had simply not dealt with the application was not sufficient to justify a legitimate expectation on the applicant's side that the application would be regarded by the EPO as still pending. The situation before the board therefore differed from the facts in J 14/94, where the EPO had actively continued the examination proceedings for several years.