Weird beaming problem with major seconds

[Chris Lipe]

Hello,

I am currently working on a piece for concert band, and am setting it 
using lilypond 1.4.11, under Red Hat Linux 7.2.  In the score, I have 
the first and second flute parts on the same line, and there's a part 
where they are both playing an eighth note ostinato, and on the offbeats 
the resulting harmony between the two is a second.  This produces some 
very odd beaming results.  I've attached a sample measure so you can 
see.  Do you know a) if this is a bug and b) if there's a workaround?  

Thanks,
Chris Lipe

FluteI = \notes {
   \clef treble
   \relative c''' {
\time 4/4 [aes8-\p( f] [aes f] [aes f] [aes )f] |
}}
FluteII = \notes {
   \clef treble
   \relative c'' {
\time 4/4 [bes8-\p( ees] [bes ees] [bes ees] [bes )ees] |
}}

\score {
<
 \context Staff = flutes
       <
   \property Staff.instrument = "Flute 1,2"
   \property Staff.instr = "Fl 1,2"
   \property Staff.midiInstrument = #"flute"
   \context Voice=one \partcombine Voice
     \context Thread=one \FluteI
     \context Thread=two \FluteII
        >

>
\paper { }
}