Like many others, I have been wondering what happened to the missing trombones and all in Bernstein's famous recording (and its original release) of Gustav Mahler's Symphony No. 9, with Berliner Philharmoniker. It was only recently that I found the following comment by someone with screen name Mezzo Corno at Amazon under Discophage's review:
"I played with the orchestra on this performance, a highlight of my career, as an "extra" horn player. The reason the trombones went silent for a bit was that a man sitting behind them in the audience, fairly close in the rows behind them, collapsed of a heart attack and died at that moment. The doctor came over and there was a bit of a buzz in the audience even as the concert continued. This event made it into the reviews of the concert the next day. That is why the trombones missed their cue.
The orchestra absolutely loved playing for Bernstein, and they were aware of the historic moment. Rehearsal photos were taken, as usual, and it seemed that every member of the orchestra bought a print of the Bernstein rehearsal photos, and stood in line to have them signed during the rehearsal. Bernstein was smoking at least 2 cigarettes at the same time, the smoke in his room thick, but man after man took his turn to thank the maestro, and to ask for his autograph on the photo. I never saw that orchestra express higher admiration for a guest conductor in the three years I was there."
Discophage then communicated this to Henry Fogel, a Fanfare Magazine critic and former President of the Chicago Symphony Orchestra for 18 years. Fogel wrote back and eventually allowed Discophage to publish his email there:
"Wow - what a fascinating story. I was aware of the trombone miss, but not the reason.
My experience with Bernstein and the Chicago Symphony was very similar (except no one died). He had not conducted the CSO before except once when he was young and not yet famous (I like to say "before he was Leonard Bernstein."). Having worked with him in New York, including a 1979 Japan tour, and the national Symphony in Washington, and having developed a good relationship with him, I immediately started working on him to come to Chicago when I went there in 1985. He kept saying that he just couldn't add another orchestra to the ones he conducted, he didn't have time, etc., and I kept begging. The musicians of the CSO knew that I was begging, and they resented it - their hubris led to the "we are the great Chicago Symphony and anyone should want to conduct us" kind of attitude. Finally, he did agree in 1988 - and I sat in the hall for the first rehearsal, to see the reaction. The musicians were skeptical, and a bit put off by the Bernstein cape and retinue (not to mention, the cigarettes). Within 5 minutes he had them eating out of his hand. And at his final concert of Shostakovich 7th (still in my view the greatest recording of that work, on DG), there they were - lined up with recordings and photos of him that they wanted him to sign (and he did - LB stayed available backstage at every single concert I ever worked with him, including in Japan where the lines are long, and signed every autograph that was requested). I did not see that with the CSO with any other conductor before or after."
So, if this is true, mystery solved!