Possible bug in partCombine

[Galen Hazelwood]

I have found a strange corner case which partCombine doesn't handle
correctly. I ran into it setting a complex orchestral score, but I've
narrowed down the demonstration to something more reasonably sized.

In this example, I have to do the known workaround in bar 2 of adding
invisible grace notes when one staff has one right after a time signature
change. The bottom line represents the piano part (with the visible
slashedGrace), the top two represent two clarinets, and the third line is a
partCombine of the first two.

Once this happens, partCombine starts putting slashes on any unison flagged
notes from that point onward. Quarter notes are fine; 8th, 16th and so on
get slashes.

The critical thing that triggers this is that one of the two combined parts
has to follow the invisible slashed grace with a flagged note, and the
other part has to be doing anything else, like rests or a quarter note.

This is simple to work around--just change the silent slashed grace notes
to silent plain grace notes--and that's what I'm doing. But it might
indicate something subtly wrong with the code, so I'm reporting this in
case anyone cares.

tiny-example.pdf
Description: Adobe PDF document

\version "2.22.2"

one = \relative c' {
	\time 4/4
	R1
	\time 2/4
	\slashedGrace s8
	e8 r4.
	e8 r4.
	e4 r4
	e8 r4.
}

two = \relative c' {
	\time 4/4
	R1
	\time 2/4
	\slashedGrace s8
	%c4 r4
	r2
	c8 r4.
	c4 r4
	c8 r4.
}

reference = \relative c' {
	\time 4/4
	c1
	\time 2/4
	\slashedGrace g8
	c2
	R2
	R2
	R2
}

\score {
	<<
		\new Staff \one
		\new Staff \two
		\new Staff \partCombine \one \two
		\new Staff \reference
	>>
}