change of behavior for cue notes in 2.23.5

[Paul Scott]

Happy New Year, all.

I thought I've always been able to get overlapping cues to work.

I have looked at the changes for 2.23.5

Why are the stem directions not working in this example?  This sometimes 
leads to:

an = \fixed c' {
                 a8 8 r4 r2 a8 8 r4 r2 }
cuecue.ly:3:18: warning: maybe input should specify polyphonic voices
an = \fixed c' {
                 a8 8 r4 r2 a8 8 r4 r2 }
cuecue.ly:5:27: warning: adding note head to incompatible stem (type = 1/8)
bn = \fixed c' { c'4 r r2
                          c'4 r r2 }
cuecue.ly:5:27: warning: maybe input should specify polyphonic voices
bn = \fixed c' { c'4 r r2
                          c'4 r r2 }

MWE:

\version "2.23.5"

an = \fixed c' { a8 8 r4 r2 a8 8 r4 r2 }
\addQuote qa \an
bn = \fixed c' { c'4 r r2 c'4 r r2 }
\addQuote qb \bn

ab = \absolute{
  \cueDuring qa #down { \cueDuring qb #up s4 } r4 r2
  << { \cueDuring qa #down s4 } \\ { \cueDuring qb #up s4 } >> r4 r2
}

\score{
  \new Staff \ab
}

TIA,

Paul