I think it is the negative review that prompted Schoenberg to write to Downes in defense of Mahler ("A person who is able to study a score ... will see all those strokes of genius, which never are to be found in the works of composers of lower mastery. One will discover them on every page of this work, in every measure, in every succession of tones and harmonies.").
Mitropoulos was famous for strange couplings. For example, he coupled Mahler's Sixth (the one recorded and released in the wonderful New York Philharmonic box of Mahler broadcast) with Gershwin's Concert in F (Bruno Walter protested for this particular coupling).