NR 3.2.3 Reference to page numbers - buggy?

[Jean-Charles Malahieude]

> Something has become buggy since version 2.12.3 and I don't know how to debug 
> it:

\book {
  \label #'firstScore         %% page 1
  \score {
    {
      c'1
      \pageBreak
      \mark A \label #'markA  %% page 2
      c'1 \label #'markTheEnd %% page 2
    }
  }

  \markup { The first score begins on page \page-ref #'firstScore "0" "?" }
%% prints page 1
  \markup { Mark A is on page \page-ref #'markA "0" "?" }
%% prints page 1
  \markup { Finish line on page \page-ref #'markTheEnd "0" "?" }
%% prints page 2
}