In T 789/95 the file contained no indication that a copy of the opponent's observations had been forwarded to the patent proprietor. It was therefore to be assumed that the communication of the observations to the patent proprietor had been omitted, in contravention of the Guidelines. In the board's view, this constituted a substantial procedural violation, as it infringed the principle that all parties to proceedings must be accorded the same procedural rights.

In J 3/87 (OJ 1989, 3) it was stated that if an EPO communication was not as clear and unambiguous as it ought to be, and led a reasonable recipient into error, that amounted to a substantial procedural violation, even if the ambiguity of the communication was partly due to an unfortunate provision of the law.