grace notes break preceding ties in MIDI

[Adam Spiers]

Hi all,

Can anyone explain the following bug, and offer a work-around?
Reproducible on latest git master:

\include "english.ly"
%\include "articulate.ly"

\score {
  \new Staff {
    \relative c' {
      % BUG: This first f~ tie will not be honoured in the MIDI output
      % due to the \grace:
      f2 ef4 f~
      % i.e. this f8 will be sounded:
      | f8 \grace c32 f4
    }
  }
  \midi {
    \context {
      \Score
      tempoWholesPerMinute = #(ly:make-moment 150 4)
    }
  }
}

If the grace note is removed, the tie works.

Thanks!
Adam