I too see this fairly regularly both at New York City Opera and New York
City Ballet.  So far as I can remember, I haven't seen it elsewhere.  While
I can understand the musicians' wanting to relieve the boredom that comes
with playing the same piece night after night, it really does look very bad
to the audience.  For that reason alone I am surprised that conductors (and
the directors of these companies) countenance it.  Why don't the players at
least put the reading material on their stands so it looks like they're
following the music?

On a couple of occasions at NYC Ballet (where the orchestra has undergone
a rapid decline since the days when Robert Irving led them), I have even
heard the brass players (of course) hold conversations audible to those
sitting upstairs!

Which reminds me of a concert I once attended featuring a new work by Edwin
London.  In the middle of it, I noticed with alarm that one of the violists
was talking at conversational level to her stand partner, as if she'd
forgotten that this was a performance, not a rehearsal.  Then I noticed
someone else in the orchestra doing the same.  Shocking!  What was going
on? More and more people began putting down their instruments and talking,
and it finally became clear that this was part of the composition, ending
with a general hubbub.  Written by somebody who has rehearsed a few too
many student groups, I would say.

Pete Caleb ([log in to unmask])