Refrain-before-verse causes extra flats to appear

[Tom Dickson]

I have a file (available at http://schnecke.bombcar.com/random/test.ly ) that 
puts extra flats after the "refrain".

If I remove the second \key bes \major line in "sopMusic" then the extra flats 
disappear, but the accidentals make it look like it's in C Major or something.

I suspect that this is the root of the problem:

                \new Staff = women <<
                        \tempo 4 = 144
                        #(set-accidental-style 'modern-voice)
                        \new Voice = "sopranos" {
                                \voiceOne \global \sopRefrain
                                        \new Voice = verse { \voiceOne 
\sopMusic }
                        }
                        \new Voice = "altos" {
                                \voiceTwo
                                        << \global \altoRefrain >>
                                        << \altoMusic >>
                        }
                >>
                \new Lyrics \lyricsto sopranos \refrain
                \new Lyrics \lyricsto verse \verseOne

I'm trying to adapt http://www.geoffhorton.com/lilypond.html#refrainfirst to 
SATB and I think I'm missing something major.

-tom