A friend told me of an incident during a BBC broadcast of "Messiah," specifically the "Hallelujah" chorus. The announcer was to make an air check at the end of "Hallelujah" and wasn't as familiar with the music as he should have been. If you don't remember how the piece ends, there are four Hallelujahs sung in quick succession, a one measure rest, then a slow syllabic "Hallelujah." 

The radio audience was treated to:

Chorus: "Hallelujah, Hallelujah, Hallelujah, Hallelujah!"
Announcer: "This is the BBC"
Chorus: "HAL-LE-LU-JAH!!!"

I'm told the conductor wasn't amused.

-- Gary Daumgldaum@umd5.umd.edu