Partcombine erratic behaviour

[Hilary Snaden]

Using version 2.16.2 on windoze, I have a chunk of (pseudo-)code like this:

\score {
  <<
    \new StaffGroup <<
      \new Staff <<
        \set Staff.soloText = #"1."
        \set Staff.soloIIText = #"2."
        \set Staff.aDueText = #"a2"
        \partcombine \flutea \fluteb
        \set Staff.instrumentName = \instrumenta
      >>
    [similar blocks for oboes, clarinets, bassoons]
    >>
  >>
}

The flute staff switches to explicit voices after two bars, the clarinet 
staff uses explicit voices throughout (both staves without full-bar 
rests in the silent parts, unless both parts are silent), the oboes and 
bassoons render as I recall partcombine working in the past.

There's nothing obviously untoward in the constituent parts, it's pretty 
straightforward early 19th-century stuff, and the log shows no warnings 
related to timing.

I recall partcombine being sometimes inflexible, but predictable and 
robust. I note that some tweaks have been added to partcombine recently, 
has its default behaviour become less robust?

--
Hilary