FingerGlideSpanner disappears if listened

[Thomas Morley]

Hi,

please consider:

mus = { b-\glide -1 b-1 }

<<
  \new Voice
    \mus

  \new Voice
    \with {
      \consists
        #(lambda (ctx)
          (make-engraver
            (listeners ((finger-glide-event this-engraver event) '()))))
    }
    \mus
>>

With most recent master out of
c3f2dddaa2b16231bc2f786fba7421f03f7da7af I get the attached image.
The FingerGlideSpanner in the second Staff disappears.
With 2.24.0 both are printed.

I've no clue what happens. Insights?

Thanks,
  Harm