partcombine/instrumentName problem

[Garrett Fitzgerald]

I have the following code in my ConductorScore.ly. The first one, with
the combined parts, doesn't print the instumentName: the second one,
with just one part, does. Anybody know offhand how to fix this?
Thanks. (Files are available at
http://www.mutopiaproject.org/cgibin/piece-info.cgi?id=1643, if that's
relevant to the answer.)

      \new Staff \with { printPartCombineTexts = ##f } {
        <<
          \set Staff.midiInstrument = "bassoon"
          \set Staff.instrumentName = "Bassoon"
          \set Staff.shortInstrumentName = "Bass."
        
          \partcombine \bassoonOne \bassoonTwo
        >>
      }

      \new Staff \with { printPartCombineTexts = ##f } {
        \set Staff.midiInstrument = "clarinet"
        \set Staff.instrumentName = "Eb Clarinet"
        \set Staff.shortInstrumentName = "Eb Clar."
        
        \clarinetInEb
      }