tempo causes insertion of empty staff line

[Philip Stolz]

> I'm not top posting.

% If tempo is specified for the whole score 
% lilypond adds an empty staff line.
% This issue did not exist in version 2.13.49.
% The first version where it occurred was 2.13.50.
% It also exists in 2.13.54.

\version "2.13.50"

\score {
   <<
    \time 4/4

    \tempo 4 = 114        

    \new Staff = "Voice" <<
      \set Staff.instrumentName = \markup {"Voice"}
      \set Staff.shortInstrumentName = #"" 

      {
        \key bes \major   
        \relative c' {bes'4 c4 d,2} \bar "|."
      }
    >>            
        
    \new PianoStaff = "Piano" <<
      \set PianoStaff.instrumentName = #"Piano"
      \set PianoStaff.shortInstrumentName = #""
      <<
        \new Staff { \key bes \major \clef treble \relative c' {bes4 c4 d2} \bar
"|."}
        \new Staff { \key bes \major \clef bass \relative c {bes4 c4 d2} \bar 
"|."}
      >>
    >>
  >>   
  
  
}