Midi block gives errors with bar number checks

[Peter Toye]

The following MWE gives bar number check errors. If you comment out the midi 
block they go away. Bizarre, but a definite bug IMHO.

 
Regards,

Peter
mailto:address@hidden
www.ptoye.com

\version "2.19.52"

\language "english"


\score {
  \new Staff {
    \repeat volta 2 {
      c''1 1
    }
    \alternative {
      { \barNumberCheck #3 d''1  }
      { \barNumberCheck #3 e''1 }

    }
    { \barNumberCheck #4 f''1 | }
  }

  \layout {
    \set Score.alternativeNumberingStyle = #'numbers
    \override Score.BarNumber.break-visibility = ##(#t #t #t)
  }

%%%%%%%%%
% comment out the midi block to remove errors

  \midi {

  }

}