Completion heads engraver

[Mike Solomon]

Does anyone know how to get the completion heads engraver assigned to one voice 
to play nicely with fractional values? Compare the two scores below:

\score {
<<
\new Staff {
  \new Voice \with {
    \remove "Note_heads_engravaer"
    \consists "Completion_heads_engraver"
  } \relative c'' {
    \time 2/4
    a1*5/8 a a a
  } }
  \new Staff \new Voice \relative c'' {
    \time 2/4
    a4 a a a a a 
  }
>>
}

}

\score {
<<
\new Staff {
  \new Voice \relative c'' {
    \time 2/4
    a1*5/8 a a a
  }
}
  \new Staff \new Voice \relative c'' {
    \time 2/4
    a4 a a a a a 
  }
>>
}
\layout { \context { \Voice \remove "Note_heads_engraver"
      \consists "Completion_heads_engraver" }
}}


I’d like the two scores to yield the result of the second one while being able 
to consists and remove engravers on a voice-by-voice basis.

Cheers,
MS