Completion_heads_engraver error

[Dan Holding]

The Completion_heads_engraver seems to cause lilypond to hang when cadenzas are
used. In the example below lilypond hangs in the Interpreting music section.

Using Debian sid, lilypond 2.8.7

\version "2.8.7"
\layout { ragged-right = ##t }

{
  \time 3/4
  \cadenzaOn
  c2 d e f g a
  \cadenzaOff
  c d e f g a
} 

\layout {
 \context {
   \Voice
   \consists "Completion_heads_engraver"
   \remove "Note_heads_engraver"
 }
}