"When I first heard performances of Bruno Walter, he quite often applied a type of Luftpause (a short wait before an especially important accent) in works of Mozart, Haydn, and Beethoven. The luftpause appears with regularity in Mahler’s scores, for it is part of his typical phrasing. It is indicated by the comma and buttressed by shortening the note before it and delaying the downbeat of the next measure ever so slightly...This nuance was noticeable in Walter's performances of the classics to such a degree that it appeared to be a mannerism, an artificiality of the kind Mahler eschewed in his more mature years. Walter too became more straight forward as he aged, revising his technique from a somewhat nervous overuse of nuance toward ever greater simplicity.” -- Erich Leinsdorf, The Composer’s Advocate, Yale 1981, p.50.

Here is an example of what Leinsdorf was referring to, at m.70-75. The text in red indicates how Walter alters the tempo.

Clips (m.70-75) The comparisons are chosen to match Walter's tempi. The luftpause is most obvious in the 1957 performance, due to the very dry acoustics. Walter Comparison 1941 mp3 Furtwängler (Dec 8 1952) mp3 1949 mp3 1957 mp3 Klemperer 1957 mp3 1958 mp3 Konwitschny 1960 mp3

Contra Leinsdorf, it appears that here at least Walter retained this 'mannerism' to the end. (I have not heard any other conductor insert a luftpause here.)