Frenched score and rehearsal marks.

[Hwaen Ch'uqi]

Greetings All,

Perhaps I have hit a bug in 2.21? When ALL staves of a StaffGroup
happen to be empty within a particular system, the rehearsal letter
continues to appear and at the top of the system. Below is code meant
to render the result.

\version "2.21"

music = \repeat unfold 5 {
  \repeat unfold 5 c'1
  \mark \default
}

rests = \repeat unfold 5 {
  \repeat unfold 5 R1
  \mark \default
}

\score {
  <<
    \new StaffGroup <<
      \new Staff {
        \rests
      }
      \new Staff {
        \music
      }
    >>
    \new StaffGroup <<
      \new Staff {
        \rests
      }
      \new Staff {
        \rests
      }
    >>
  >>
  \layout {
    \context {
      \Score
      \remove "Mark_engraver"
      \remove "Staff_collecting_engraver"
    }
    \context {
      \StaffGroup
      \consists "Mark_engraver"
      \consists "Staff_collecting_engraver"
    }
    \context {
      \Staff
      \RemoveEmptyStaves
    }
  }
}

I gladly point out that this is already a marked improvement over
2.20, where moving "Staff_collect_engraver" to the StaffGroup context
resulted in all rehearsal/tempo marks atop the uppermost staff. Thank
you for any suggestions/input.

Hwaen Ch'uqi