'Translation' of a current @knownissue for \partcombine

[James Lowe]

Hello,

Can someone explain in more simple terms (perhaps with an example) what

--snip--
@code{\partcombine} only observes onset times of notes.  It cannot
determine whether a previously started note is playing or not, leading
to various problems.
--snip--

means?

I'm just making a new patch to tidy this section up and add a new @known and if 
someone can enlighten me on this rather cryptic para, I could update that for 
mere mortals like myself.

Thanks for your time.

James