in concert, i'd say 'no, it's fine'; in a show, i'd say 'yes, definitely, it's wrong'. it breaks the line, interrupts the flow. to applaud a star entrance seems silly to me, but it happens all the time & the convention is already established. there are also well-known showstoppers, like 'mama's turn' & a # in 'boy from oz' which has mercifully escaped me, but it's the last song before 'i go to rio'. sorry 'bout no caps -- hurt wing.
Murder By Music at Dillons 9/9, 16, 23, 30
www.murderbymusic.com