beaming problem in 2.14

[Stefan Thomas]

Dear community,
the following code works fine in 2.12.3. but doesn't in 2.14.1.
Is there a possibility to get it working in 2.14.1?

\version "2.14.1"

music = {
  \clef bass r2 r4 r8 f, 
  r2 r4 g,8 r 
  r4 f, 8 r8 r2
}

beams = {
  \repeat "unfold" 24 { s8[ s ] s[ s]} % this line causes the error!
}

\new Staff {
  \context Voice << { \beams } { \music}>>
}