parallel music with selective repeats

[Patrick or Cynthia Karl]

I have a piece of music that needs to have all staves but one repeat, and that 
non-repeating staff is twice as long as the repeating.  I tried the following 
but got no joy:

 \version "2.19.15"

musicA = \relative b' { c d e f }
musicB = \relative f'  { f e d c }

\score {
    <<
        \new Staff { \musicA \musicB}
        \new ChoirStaff 
            <<
                \new Staff { \repeat volta 2 \musicA }
                \new Staff { \repeat volta 2 \musicA }
            >>
   >>
    \layout {}
    \midi {}
}

The repeat bar is in all three staves, with musicB following on the first staff.

If I add the "unfoldRepeats" command to the score, all three stave in the pdf 
are as I wish, and the midi file agrees.

I have tried a couple of things to suppress the repeat bar line on the first 
staff:

  * adding \bar "|" between musicA and musicB
  * adding \set Score.repeatCommands = #'(#f) both before and after \musicA in 
the 1st staff
  * adding \with { \remove "Volta Engraver" } to the first staff

but the repeat bar is printed in the 1st staff every time.

Is there a way to suppress that repeat sign?  How?