engraving ends too early

[Dan Eble]

% 2.19.20 does not engrave the lyrics and stops engraving the vocal
% staff before the end.  (Compare to 2.18.2.)  I haven’t tested MIDI.

\version "2.18.0"
\include "english.ly"

vocal = \relative c'' { R1 | f2 c }

% adding the skip makes 2.19.20 work
accomp = \relative c'' { c1 %{ s1 %} }

\score {
  <<
    <<      
      \new Staff <<
        \new Voice = "vocal" { \vocal }
      >>
      \new Lyrics <<
        \lyricsto "vocal" { \lyricmode { La la } }
      >>
    >>
    
    \new Staff <<
      \context Voice = "obligII" { \accomp }
    >>
  >>
}