Overlapping notes and midi output

[Hinrik ÖrnSigurðsson]

When I have overlapping notes in a song, they will both be heard in the midi
output if they are on separate staffs (see the first measure in my code
example). But if they occur on the same staff, the latter one is not heard (see
the second measure).

I'm using timidity+pmidi on Linux. Is this a bug in lilypond's midi output or is
there something wrong with the midi player I'm using? Timidity's --overlap-voice
option has no effect on this issue.

Gmane's web form seems to think I'm top-posting no matter where I place my code
example, so I've pasted it here: https://gist.github.com/867886