would this qualify as a bug (in partcombine)?

[arie-lily]

I extracted the following strange behaviour in \partcombine, with this
snippet it works well:

\version "1.6.10"
\score {
    \context Voice = voiceOne {
        \partcombine Voice
        \context Thread = threadOne \notes \relative c { c8 d e }
        \context Thread = threadTwo \notes \relative c { e8 d g }
    }
}

That is to say: ly2dvi complains about (and consecutively ignores them)
clashing notecolumns, but displays the music correctly.
However, when I change 
\relative c
into
\relative c'
or
\relative c''
(of course both of them have to be changed at the same time with the
same amount), then the stems of the third notes are both printed.
I think this must be a bug, not?

arie - just asking before filing a bug report for nothing...