inconsistent bar number placement

[Juan Cristóbal Cerrillo]

Dear all,

I’m having trouble understanding why the barnumber in measures 5, 6, 9 and 10 
in the following example are placed so differently as the other bar numbers.
What causes this behaviour?
Any help would be greatly appreciated.

all best,

jc

\version "2.18.2"

\layout {
  \context {\type "Engraver_group"
            \consists "Time_signature_engraver"
            \consists "Axis_group_engraver"
            \name "TimeSig"
            \alias "Staff"
            \override TimeSignature.style = #'numbered
            \override TimeSignature.font-size = #6
            \override TimeSignature.break-align-symbol = ##f
            \override TimeSignature.X-offset =
            #ly:self-alignment-interface::x-aligned-on-self
            \override TimeSignature.self-alignment-X = #CENTER
            \override TimeSignature.after-line-breaking =
            #shift-right-at-line-begin
  }
  \context {\Score
            \accepts TimeSig
            tupletFullLength = ##t 
  }
  \context {\StaffGroup
            \accepts TimeSig         
  }
  \context {\Staff
            \remove "Time_signature_engraver"
            tupletFullLength = ##t        
  }
}

music = \relative c''
{
  \tupletUp
  \repeat unfold 5 {
    \time 4/4
    \tuplet 3/2 {
      c2 c c 
    }\pageBreak
    \time 3/4
    \tuplet 4/3 {
      c,,4 c c c
    }
    \break
  }
}

\score {
  \new StaffGroup 
  <<
    \new TimeSig 
    \new Staff \music
    \new Staff \music
  >> 
}