midi not rendering tied notes

[Bruce Pike]

I'm having difficulty getting midi generation to recognize tied notes.  For the score below, when I play the midi output the notes sound as individual eighth notes rather than as tied notes.

\version "2.18.2" \language "english"

music = \relative c {
  \time 4/4 \key c \major
  e'8 g( g) g( g) e( e) a |
}

\score {
    \new Staff
    { 
      \music      
    }
  \layout { }
  \midi { } 
}

BruceP