Partcombiner eats up rests

[Rutger Hofman]

Hi folks

Sorry if I missed any changes between my Lily version (2.8.8.) and the 
bleeding-edge version. But here goes:

I stumbled into behaviour that I think is a bug in the PartCombiner. In 
the case where one of the two parts is (temporarily) silent and the 
playing voice has a rest, the rest is not printed.

I attach a lily snippet that shows the incorrect output, and a version 
that shows it is easy to work around (replace s with r in the silent voice).

Rutger Hofman
Amsterdam

P.S. Some background: I know, PartCombiner wants both voices to be 
unisono in order to print only one. But the piece I was typing in wanted 
differently: at certain moments one of the 2 players must switch to 
another, also existing, voice. In this sense it is more like cue notes.
\version "2.7.40"

\paper {
    ragged-right = ##t
}

\new Staff {
    \set Staff.printPartCombineTexts = ##f
    \partcombine
    { s2 g'4 a' }
    { r4 g' b' c' }
}


\new Staff {
    \set Staff.printPartCombineTexts = ##f
    \partcombine
    { r4 s4 g'4 a' }
    { r4 g' b' c' }
}