rhythmic-location reports wrong measure with Score.currentBarNumber

[uliska]

This is the actual issue behind openlilylib/scholarly#67.

\version "2.19.82"

#(define (rhythmic-location grob)
   "Return the musical/rhythmical position of a given grob
    as a pair of a measure number and a moment in that measure.
    If the position can't be determined return an 'impossible'
    value in measure 0."
   (if (ly:grob? grob)
       (or (grob::rhythmic-location grob)
           (cons 0 (ly:make-moment 0/4)))
       (ly:error "Requested rhythmic-location of a grob, but ~a is not a grob," grob)))

{
  \override NoteHead.after-line-breaking = 
  #(lambda (grob)
     (ly:message "Location: ~a" (rhythmic-location grob)))
  c'1
  \set Score.currentBarNumber = 12
  c'1
}

prints

Location: (1 . #<Mom 0>)
Location: (2 . #<Mom 0>)

(instead of 1 and 12).

Obviously this is due to grob::rhythmic-location, and I'll ask on bug-lilypond whether that's a bug or wrong usage.