Uncontrollable \mark

[Will Oram]

This is sort of a repeat from many months ago. It might be a bug; it  
might not.

Try running the snippet below. The result is that \mark on the top  
line is placed as expected; \mark attached to GrandStaff is pushed  
way too far to the left. Any attempt to manipulate the second \mark's  
position fails, and you only end up moving around the top heading. So  
\override Score.RehearsalMark #'break-align-symbol = #'whatever  
doesn't work, at least in the gazillion spots I've stuck it.

markGroup = {
        \mark \markup {Hyper-Allegro.}
}

\score {
<<
                \new Staff <<
                        \markGroup
                        \new Voice { c'1 | c' }
                >>
        
                \new GrandStaff <<
                    \new Staff \with { \consists "Mark_engraver" } <<
                                \markGroup
                                \new Voice { c'1 | c' }
                        >>
                        
                        \new Staff <<
                                \new Voice { c'1 | c' }
                        >>
                >> % end GrandStaff
>>

\layout {
        \context { \RemoveEmptyStaffContext }
        \context { \GrandStaff \consists "Instrument_name_engraver" }
}
}

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