No pdf marks with bookparts?

[Thomas Morley]

Hi,

the following code generates outlined nested pdf-marks, see attached.

\version "2.21.4"

\book {
  \markuplist \table-of-contents
  \tocItem x #"foo"
  \tocItem x.y #"foo-1"
  { R1 }
}

Though, if I switch from \book to \bookpart pdf-marks are gone (while
the table-of-content is still unaffected).

Any hints how to keep pdf-marks displayed?

Thanks,
  Harm