It is necessary to welcome the publication of the paper by Park and Bongiorno Jr (Park, K. and Bongiorno Jr, J.J. (2009), 'Persistent Inputs and the Standard H-2-multivariable Control Problem', International Journal of Control, 82, 2002-2012) in which the special cases in H-2-optimisation problems are considered. However, for correct orientation of readers we would like to note some publications which, in our opinion, are connected to a problem given by Park and Bongiorno Jr (2009), but are absent there.